Convenient synthesis and cycloaddition reactions of 2

Convenient synthesis and cycloaddition reactions of 2-phenylseleno-1,3-butadiene and 2-trialkylstannyl-l,3-butadienes GORDONS. BATES,'MICHAEL D. F R Y Z U K ,A' N~D~ CHARLES STONE Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T l Y 6 Received May 20, 1987

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GORDON S. BATES,MICHAEL D . FRYZUK, and CHARLES STONE. Can. J. Chem. 65,2612 (1987). The facile preparation of 2-trialkylstannyl-l,3-butadienesand 2-phenylseleno-1,3-butadieneby reaction of 2-(1,3butadieny1)magnesium chloride with trialkylstannyl chlorides and phenylselenium chloride, respectively, is reported. The Diels-Alder reactivity of these dienes with a variety of activated dienophiles is also described. Finally, a novel transmetallation of tin, in vinyl stannanes, to selenium by use of phenylselenium chloride is outlined. GORDON S. BATES,MICHAEL D . FRYZUK et CHARLES STONE.Can. J. Chem. 65,2612 (1987). On rapporte une mCthode facile de prtparer les trialkylstannyl-2 et phCnylsC1Cno-2 butaditnes- 1,3 qui implique la reaction du chlomre du butadikne-1,3 yle-2 magntsium avec les chlorures soit de trialkylstannyles soit de phCnylsC1Cnium. On dCcrit aussi la rCactivitC de ces dienes, dans la reaction de Diels-Alder, avec divers diknophiles actives. Enfin, on dCcrit une nouvelle rCaction de transmCtallation de I'ttain, dans des stannanes de vinyles, vers le selenium du chlorure de phenylstlCnium. [Traduit par la revue]

Introduction As part of our interest in the Diels-Alder reactivity of 1,3-dienes with metalloid (1) or transition metal substituents, we have examined the synthesis of 2-substituted 1,3-butadienes of the formula 1 (ML, = metalloid or transition metal complex). Our rational approach was to use the readily available, inexpensive starting material chloroprene 2, and examine its conversion to 1 via the Grignard reagent 3. It had been reported that attempts to prepare 3 from chloroprene gave polymers; however, the preparation of this Grignard reagent could be achieved from the less accessible 4-chloro1,2-butadiene (2). More recently, a modification was published that allows 3 to be prepared directly from 2 by first activating the magnesium (3). We have used this procedure to prepare 2trialkylstannyl-1,3-butadienes4 and 2-phenylseleno- 1,3-butadiene 5 in a one-step, facile synthesis. While our work was in progress, reports on alternative syntheses and Diels-Alder reactivity of 4 and 5 were communicated. A "tin-cupration" of 2-butyne-1,4-diol followed by "silyl-cupration" generated 4 a in reasonable yield (4), while an equally elaborate Wurtz-type coupling yielded 4b (5). The preparation and isolation of 5 have never been reported to our knowledge, although the synthesis of the SO2-masked derivative 6 has been recently described along with a study of its Diels-Alder reactivity (6). In this paper we describe the following: (i) full details for the one-pot synthesis of 4 and 5, (ii) cycloaddition reactions of

' ~ u t h o r sto whom correspondence may be addressed. 'Fellow of the Alfred P. Sloan Foundation (1984- 1987).

these dienes with a variety of dienophiles, and (iii) the first example of transmetallation from tin to selenium.

Results and discussion Synthesis of dienes Chloroprene 2 is readily converted to the corresponding Grignard reagent 3 by activating the magnesium with 1-3 mol% anhydrous ZnC12 and small amounts of 1,2-dibromoethane. In this fashion, 0.25-0.60 M solutions of 3 in tetrahydrofuran (THF) can be obtained. The subsequent reaction with the commercially available stannyl halides and phenylselenium chloride provides for the convenient, one-pot preparation of the dienes 4 and 5 on a multi-gram scale (see eq. [I]). Diene 5, previously uncharacterized due to its ready polymerization (6), was isolated and found to be stable for long periods at low temperature ( - 20°C). Diels-Alder reactions Reaction of 2-trialkylstannyl-l,3-butadienes4 with a variety of activated dienophiles leads to the preparation of substituted cyclohexenes containing a vinyl stannane functionality. This latter functionality has been shown to have great synthetic potential via transition metal catalysed cross-coupling with vinyl halides (7) and vinyl triflates (8). The results of the preparation of such trialkylstannyl-substituted cyclohexenes 7-11 are summarized in Table 1. In general, the reactions proceeded smoothly at elevated temperatures to give good yields of the Diels-Alder cycloadducts. However, reaction of 4a with maleic anhydride for extended periods of time at room temperature gave the best yields of cycloadduct 7. In the work-up of 9, by column chromatography on silica gel, enolization took place producing small quantities of the corresponding hydroquinone. Hydroquinone production was also observed when reaction times in excess of 12 h were used. Similar results were noted in the preparation and work-up of 14 (see Table 2), albeit to a lesser extent. The trialkylstannane substituted diene allows for facile reaction with electron-deficient dienophiles, as is evidenced by its ready cycloaddition with dimethyl acetylenedicarboxylate. Extended periods (several days) of reflux in toluene with diphenylacetylene, an electron-rich dienophile, led only to isolation of starting materials. In an attempt to determine the directing effect of the stannyl

BATES ET AL

TABLE1. Reaction of 2-trialkylstannyl- l,3-butadienes 4 a / 4 b


Entry

Dienophile

Conditions

Products

Yields

C02Me

PhCH,, reflux, 18 h

71 % n-Bu3Sn

11 a

C02Me

llb

ClMg

3

moiety, the reaction of 4b with methyl acrylate at reflux in toluene was examined. In analogy to results previously observed in cycloaddition reactions of silylbutadienes (9), the stannyl moiety was found to exhibit only a weak directing effect, resulting in a 2:l mixture of para:meta regioisomers l l a : l l b . 3 Other workers have shown (46) that the use of 15% 3 ~ hbest e yields of l l a / l l b were obtained by use of several equivalents of freshly distilled methyl acrylate containing 2 mol% (based on diene) 2,6-di-tert-butyl-4-methylphenol (BHT).

A1Et2Cl in the reaction of 4 a with ethyl acrylate gave a 10:l ratio of para:meta regioisomers. The assignment of l l a (para) as the major regioisomer is based on much literature precedent, both theoretical and experimental (6, 10). Attempts to separate mixtures of l l a / 11b using column chromatography proved difficult; however, an enriched 7:l ( 1 l a : l l b ) mixture was obtained. It was hoped that by use of 'H nrnr NOEDIFF (nuclear Overhauser effect difference) spectroscopy (1 l), on this enriched mixture, more physical evidence for the assignment of the major regioisomer

CAN.J. CHEM. VOL. 65, 1987

TABLE2. Reaction of 2-phenylseleno-l,3-butadiene5 Entry

Dienophile

Conditions

Products

Yields

PhCH,, room temp., 2 days

1

70%

PhSe

12

0


2

0

PhCH,, reflux, 8 h

(N-ph

76% PhSe

0

13

O

CO, Me

4

MeO,CC=

CC0,Me

PhCH,, reflux, 1 8 h

81 % PhSe

C02Me

15

PhCH,, reflux, 1 8 h PhSe

16a

16b

4:l

could be achieved. Unfortunately, the results of such experiments at 400 MHz were equivocal. The results of the cycloaddition reactions of the phenylseleno diene 5 with a variety of activated dienophiles are outlined in Table 2. The reaction of 5 at room temperature with maleic anhydride and at elevated temperature with less activated dienes yielded cycloadducts 12-16.4 The synthetic utility of the vinyl selenide functionality is realized most readily in its role as a masked carbonyl(12). Other uses involve cross-coupling reactions with Grignard reagents in the presence of nickel-phosphine catalysts (13) and oxidative cleavage with hydrogen peroxide (14). Evidence that the selenenyl substituted diene permits facile reaction with electron-deficient dienophiles is seen in the ready formation of 12-16 and in its total lack of reactivity with diphenylacetylene. Regiochemical investigation of the Diels-Alder reactivity of 5 involved reaction with methyl acrylate at reflux in toluene. A 4:l mixture5 of para:meta regioisomers was obtained in excellent chemical yield. This result was in complete agreement with published data, based on theoretical calculations, on the products obtained by reaction of 6 with ethyl acrylate (6). The --

4Addition of 2 mol% (based on diene) BHT was used in all reactions of 5. 5 ~ attempt o was made to separate this mixture.

results of our study show that, in reaction with methyl acrylate, the selenenyl moiety has a greater directing effect than the stannyl substituent.

Transmetallation from tin to selenium Other results from our laboratory (1) have shown that addition of phenylselenium chloride (PhSeCl) to solution of zirconium dienyl complexes results in smooth transmetallation from zirconium to selenium with immediate discharge of the deep red colour of PhSeCl. A similar result was obtained when the stannyl diene 46 was reacted with PhSeCl at room temperature (see eq. [2]). Work-up of the reaction mixture yielded a yellow oil that had identical spectral data to diene 5, indicating that the transmetallation reaction had proceeded without rearrangement. In an attempt to gain further comparative information on the reaction of the dienes 4 a and 5 with methyl acrylate, a solution of PhSeCl was added to a 2:l para:meta mixture of the Diels-Alder adducts l l a l 11 b . Stimng the mixture overnight at room temperature caused discharge of the deep red colour of the PhSeC1, which on work-up yielded a 2: 1 para:meta mixture of 16a/16b as determined by 'H nmr (see eq. [3]). This result indicates that the major regioisomer formed in reaction 4b and 5, with methyl acrylate, was the same in each case. Transmetallation of tin in vinyl stannanes has precedence in

BATES ET AL

[21 Me,Sn

X

RT

+

PhSeCl

toluene (-Me,SnCI)

PhSe

4b

-C02Me

PI

5

+

RT

toluene (-Me,SnCI)

Me, S n


PhSeCl

Ilolllb 2:1

para: meta reactions at low temperature with alkyl lithium reagents (15), and in coupling reactions catalysed by palladium complexes (7). Stereoselective transmetallation from mercury to selenium by reaction of vinyl mercuric compounds with PhSeCl has also been observed (16). The reaction of vinyl stannanes with PhSeCl is analogous to a previously reported reaction in which iodine is used to cleave the tin-carbon bond producing a vinyl iodide (17). Much work has already been done on the mechanism of areneselenenyl chloride addition to alkenes. Schmid and Garratt (18) have proposed three possible mechanisms, which differ only in the relative amount of carbon-selenium bond making and selenium-chlorine bond breaking leading up to the formation of the seleniranium ion. In our system, collapse of seleniranium ion 17 to give diene 5 could proceed via attack of chloride at the

least-substituted carbon or at tin, followed by elimination of ~ e ~ ~ n No C 1spectroscopic . ~ evidence for the formation of allenic species was observed. This transmetallation reaction appears to be general for vinyl stannanes. It exhibits interesting chemoselectivity as shown in eq. [2], with no products of addition to the isolated double bond being observed. To our knowledge, this is the first example of transmetallation from tin to selenium. Further studies in this area will involve investigation of the stereochemistry of this metal-transfer reaction.

Experimental The 'H nmr spectra were recorded on a Bruker WH-400 equipped with Aspect 2000 computer software. Signal positions are given in delta (6) with reference to C6D5H at 7.15 ppm. Infrared spectra were run on a Nicolet 5D-X spectrophotometer. Low resolution and high resolution mass spectra (hrms) were determined on a Kratos MS-50 spectrometer. Gas-liquid chromatography was performed on a Hewlett-Packard model 5880a gas chromatograph using a 12 m X 6~ similar argument is put forward to explain the stereospecific cleavage of an E / Z mixture of PhCH=CHSnMe3 by Br2 (19).

k>-

C02Me

PhSe

16011 6 b 2:l

para: meta 0.2 rnm column (Carbowax 10M). Column chromatography was carried out using Merck Kieselgel 60 (230-400 mesh ASTM). For thin-layer chromatography (tlc) silica gel 1318 1 (Eastman chromagram) sheets were used. Microanalyses were performed by Mr. P. Borda, Microanalytical Laboratory, University of British Columbia. Dry solvents were used in all experiments. Tetrahydrofuran (THF) and toluene were dried by refluxing over and then distilling from sodium-benzophenone ketyl. All Diels-Alder reactions were carried out in the absence of light. In addition, reactions of 5 and reactions involving methyl acrylate contained 2 mol% (based on diene) 2,6di-tert-butyl-4-methylphenol (BHT). No microanalysis is given for previously prepared compounds. For cycloadduct 9, satisfactory microanalysis could not be obtained; instead, hrms is given for the hydroquinone. Grignard reagent 3 was prepared according to Method A in ref. 3. 2-Tri-n-butylstannyl-1,3-butadiene, 4a Tri-n-butyltin chloride (14.64 g, 45 mmol) dissolved in 25 mL THF was added dropwise, at room temperature, to a stirred solution of Grignard 3 (75 mL, 45 mmol; 0.6 M solution in THF) under nitrogen. The mixture was stirred at room temperature for a further 6 h, and then 10 mL of water was added to decompose any unreacted Grignard reagent. At this stage most of the THF was evaporated, leaving a white sluny that was extracted with 3 X 100 mL portions of diethyl ether. The ether layer was washed with 2 X 100 mL portions of aqueous 2 M potassium fluoride to remove any unreacted n-Bu3SnC1. Finally, the organic layer was washed with 2 X 100 mL water and dried over anhydrous MgS04. Evaporation of the solvent and distillation under Torr; 1 Torr = high vacuum yielded one fraction (40-50°C/ 133.3 Pa) of a colourless liquid 4a (10.9 g, 71%). Spectroscopic data for 4a were consistent with those reported in ref. 4a.

2-Trirnethylstannyl-I ,3-butadiene, 4 b Trimethyltin chloride (6.0 g, 30 mmol) dissolved in 25 mLTHF was added dropwise, at room temperature, to a solution of Grignard 3 (50 mL, 30 mmol; 0.6 M in THF) under nitrogen. The mixture was stirred at room temperature for a further 6 h. The work-up was identical to that described for 4a. Distillation, at reduced pressure, yielded 4b (4.35 g , 65%) as a colourless liquid, distilling at 42OC/ 11 Torr. ~ ~ e c t r o s c o ~data i c for this -compound were identical to those reported in ref. 5. 2-Phenylseleno-1,3-butadiene, 5 Phenylselenium chloride (4.78 g, 25 mmol) dissolved in 25 mL THF was added dropwise, at room temperature, to a stirred solution of Grignard 3 (100 mL, 25 mmol; 0.25 M in THF) under nitrogen. The deep red colour of the PhSeCl dissipated immediately on addition to 3; the reaction was then stirred at room temperature for a further hour. The work-up was identical to that described for 4a, with the omission of the aqueous KF washings. After drying the organic layer, evaporation of the solvent yielded a yellow oil. Distillation of the latter under high


2616

CAN. I. CHEM. VOL. 65, 1987

Preparation of 12 vacuum (lop3Torr) gave a pale yellow oil 5 (3.66 g, 70%); v,,, (film): Asolutionof 5 (750 mg, 3.59 mmol) and maleic anhydride (351 mg, 1620, 1572, 1477, 1439, 1214, 914, and 735 cm-I; 6 (C6D6, 400MHz):5.00(1H,d,J= 10.5Hz),5.34(lH,s),5.53(lH,s),5.623.59 mmol) in 3 mL toluene was stirred at room temperature for 48 h under nitrogen. A mass of white crystals gradually deposited from (lH,d, J = 17Hz),6,24(1H,dd,J = 10.5Hz, 17Hz),6.94(3H,m), solution. Low temperature recrystallization of this material (from and 7.44 (2H, m). Anal. calcd. for CloHloSe:C 57.43, H 4.82; found: ether/petroleum ether) yielded pure 12 (771 mg, 70%); v,,, (Nujol): C 57.66, H 4.81. 1845, 1780, 1245, 1010, and 942 cm-'; 6 (C6D6, 400 MHz): 1.42 Preparation of 7 (lH,m), 1.76(1H, m),2.04(1H, m),2.11 ( 2 H , m ) , 2 , 3 7 ( 1 H , m ) , A solution of 4a (500 mg, 1.46 mmol) and maleic anhydride 5.61 (lH, m), 6.97 (3H, m), and 7.33 (2H, m). Anal. calcd. for (143 mg, 1.46 mmol) in 2 rnL of toluene was stirred at room temperaCI4Hl2O3Se:C 54.74, H 3.94; found: C 54.56, H 3.92. ture under nitrogen for 48 h. The solvent was evaporated and the Preparation of 13 residue was purified directly by column chromatography (eluent: A solution of 5 (1.00 g, 4.78 rnmol) and N-phenylmaleirnide ether/petroleum ether 1:2) yielding 7 (482 mg, 75%) as a white solid. (829 rng, 4.78 rnrnol) in 3 rnL toluene was refluxed for 8 h under Spectroscopic data for 7 were identical to those reported in ref. 4a. nitrogen. The solvent was evaporated and the residue was chromatoPreparation of 8 graphed (eluent: ether/petroleum ether 1:3) to give 13 as a yellow oil A solution of 4a (500 mg, 1.46 mmol) and N-phenylmaleirnide (1.39 g, 7670); v,,, (film): 1960, 1882, 1782, 1715, 1597, 1575, (252 mg, 1.46 mrnol) in 3 mL of toluene was refluxed for 8 h. The 1384, 1180, and 745 ern-'; 6 (C6D6, 400 MHz): 1.75 ( l H , m), 2.08 solvent was evaporated and the residue was subjected to column (lH,m), 2.40(2H,rn),2.49(1H, m),2.78 (IH, rn), 5.92(1H,m), and chromatography (eluent: ether/petroleum ether 1:3), which yielded 8 6.98-7.50 (lOH, m). Anal. calcd. for C20H17N02Se: C 62.83, H 4.48, (675 mg, 9070) as a yellow oil; v,,, (film): 1779, 1712, 1499, 1456, N 3.66; found: C 62.91, H 4.63, N 3.80. 1378,1190, 1171,and690crn-';6(C6D6,400MHz):0.90(15H,m), Preparation of 1 4 1.29 (6H, rn), 1.48 (6H, m), 1.84 (IH, rn), 1.99 ( l H , m), 2.53 A solution of 5 (657 rng, 3.14 mrnol) and benzoquinone (340 mg, (2H, rn), 2.63 (lH, dd, J = 6 H z , 15 Hz), 2.85 (lH, d, J = 15 HZ), 3.14 rnrnol) in 2 mL toluene was refluxed for 2 h under nitrogen. Upon 6.01 (lH,rn),7.00(lH,m),7.15(2H,m),and7.41 (2H,m).Anal. cooling the reaction to room temperature a white solid deposited. After calcd. for C26H39N02Sn:C 60.49, H 7.61, N 2.71; found: C 60.60, evaporation of the bulk of the solvent the residue was dissolved in H 7.79, N 2.60. CH2C12and passed through a short column (2 cm X 2 cm) of silica Preparation of 9 to remove small traces of a highly coloured material. Removal of the A solution of 4a (500 mg, 1.46 mmol) and benzoquinone (158 rng, solvent and recrystallization from toluene/petroleum ether yielded a 1.46 mmol) in 3 mL toluene was refluxed under nitrogen for 5 h. white solid 14 (638 mg, 64%); v,,, (KBr): 1676, 1598, 1577, 1475, The solvent was evaporated and the residue was purified by column 1435, 1263, and 737 crn-'; 6 (C6D6, 400 MHz): 1.68 (lH, m), 2.05 chromatography (eluent: dichloromethane) to give 8 as a yellow oil (IH, m), 2.17 (IH, m), 2.41 (2H, m), 2.59 (IH, m), 5.87 ( l H , rn), (453 rng, 69%); v,,, (film): 1684, 1602, 1260, 1090, and 850 cm-'; 5.92 (lH, s), 5.93 (IH, s), 7.00 (3H, m), and 7.47 (2H, m). Anal. 6 (C6D6,400 MHz): 0.90 (15H, rn), 1.32 (6H, m), 1.32 (6H, m), 1.54 calcd. for Cl6HI4o2Se:C 60.58, H 4.45; found: C 60.56, H 4.52. (6H, m), 1.84 (lH, rn), 2.17 (lH, rn), 2.39 (lH, rn), 2.57 (lH, m), Purification of 14 using long columns of silica (> 10 cm X 2 crn) led 2.63 (IH, m), 2.70 (lH, m), 5.72 (lH, m), and 6.05 (2H, s). From to significant decomposition, as well as formation of small quantities the chromatography of 9 a white solid (53 mg, 8%) was obtained, (generally