J. Org. Chem., Vol. 43, No. 8, 1978
Vinylcyclopropene Photochemistry
1493
Vinylcyclopropene Photochemistry: Photochemistry Applied to Organic Synthesis. Exploratory and Mechanistic Organic Howard E. Zimmerman* and Steven M. Aasen Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706 Received October 4 , 1977
3 .Vinylcyclopropenes have been found to rearrange photochemically to afford cyclopentadienes. The reaction is of both synthetic and mechanistic interest. Direct irradiation of 3-vinyl-1,2,3-triphenylcyclopropene led to 1,2,3triphenylcyclopentadiene, 3-(l-phenylvinyl)-l,2,3-triphenylcyclopropenegave 1,2,3,4-tetraphenylcyclopentadiene, and 3-isobutenyl-1,2,3-triphenylcyclopropene yielded 1,2,3-triphenyl-5,5-dimethylcyclopentadiene and 3isobutenyl-I ,2-diphenylindene in a 2.5:l ratio, while 3-isobutenyl-1,3-diphenyl-2-tertbutylcyclopropene afforded
l-tert-butyl-2,3-diphenyl-5,5-dimethylcyclopentadiene, 1,3-diphenyl-2-tert-butyl-5,5-dimethylcyclopentadiene, 1,2-diphenyl-3-tert-butyl-5,5-dimethylcyclopentadiene,and 3-isobutenyl-1-tert-butyl-2-phenylindene in a 3:1:4:3 ratio. Similar photolysis of 1,2,3-triphenyl-3-methylcyclopropene gave 3-methyl.1,2-diphqn$i~e;.;wfiile irradiation of 1-methyl-2,3,3-triphenylcyclopropene produced l-methyl-2,3-diphenylindene. Sefi8&ht3wk,t.qk vinylcyclopropenes led to product only in the case of the isobutenyl-substituted cyclopropenes; the vinyl-bearing molecules were unreactive. Quantum yields were determined for direct and sensitized runs, and where triplet reactivity resulted the sensitized efficiencies were slightly more than tenfold greater than the direct rua quantum yields. The results revealed a competing vinyl walk reaction in appropriately substituted reactants. This arises from an incipient di-n-methane rearrangement. A trend of quantum efficiencies was observed in which terminal 6 y l substitution on the vinyl group inhibits reactivity. Similarly, phenyl substitution a t the a carbon of the vinyl group was found to enhance reactivity. Finally, phenyl substitution a t carbon 1of the cyclopropene ring enhaneed the reaction efficiency. Regioselectivity was encountered when the cyclopropene a- bond was unsymmetiidy+M,&uted. Here preference is for new carbon to carbon bond formation a t the three-ring r-bond position bear@ +e alkyl rather than the aryl group. The cyclopentadiene-forming reaction proved to be more efficient than indene Eormation and dominates where both are a priori possibilities. Carbene and diradical mechanisms are consider&.
One of the most general of photochemical reactions is the di-a-methane r e a ~ ~ a n g e m e nWe t . ~have been more broadly interested in the photochemistry of molecules containing two x moieties. Our investigations have led us to a study of vinylcyclopropenes. For this study we selected cyclopropenes having some aryl substitution on the three-ring A bond and substitution at the carbon (i.e., C-3) bearing the vinyl group. We were interested in the type of photochemistry observed, in the effect of substitution on the reaction course and reaction efficiency, and in the mechanisms of reactions encountered. Synthesis of Photochemical Reactants. 3-Vinylcyclopropenes have not been reported previously in the l i t e r a t ~ r e . ~ reSyntheses are outlined in Chart I, following the
action of organomagnesium compownds with a cyclopropenium salt. In the preparation of tert-butylcyclopropene 5, no butylcyclopropene trace of 3-isobutenyl-1,2-diphenyl3-tert(6), an a priori product of the reaction, was detectable. Presumably steric hindrance presented a kinetic barrier to formation of this isomer. Two non-vinyl-substituted cyclopropenes, desired for comparison purposes, 1,2,3-triphenyl-3-methylcyclopropene ( 11)6and l-methyl-2,3,3-triphenylcyclopropene (12), also were obtained as outlined in Chart I.7,8 Exploratory Photolyses of the Vinylcyclopropenes and Proof of Product Structures. Irradiation of 3-vinyl-1,2,3triphenylcyclopropene (3a) in tert-butyl alcohol using a 450-W medium-pressure lamp and a Pyrex filter for 3.25 h
Chart I. Synthesis of Vinylcyclopropenes
R2
Ph
Ph
1
2a-c
Ph
3a-c Nan, hv diglyme, pentane
NH,NHTs.MeOH
Ph
Ph
px
-
Ph
P
-Me ,C=CHMgBr
px t-Bu
I
L _ _ _
Ph 10
9
Ph PhMgBr
-
(no 6 )
Ph
Ph
Ph,CBF,
;Pfa.
5
0022-326317811943-1493$01.00/00 1978 American Chemical Society
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f2
+
pb&
h
t
I1
1494 J. Org. Chem., Vol. 43, No. 8, 1978
Zimmerman and Aasen
afforded 1,2,3-triphenylcy~lopentadiene~ (13)in 87% yield, identified by the physical data and by independent synthesis. The photoreaction can be depicted as in eq la.
Chart 111. Synthesis of the Cyclopentadienes
f l ' 1 ro
r Al/Hg P
h
G
E
EtOH-H,O
Ph
Ph
OH
OH 18
17
13
3a
@ direct 4, sens
pyridine
Ph
0.027 4,6.25.6.83, 6.70, 6.77, 6.90, 7.20,7.42, 7.85,8.13, bonate, water, and saturated aqueous sodium chloride. The dried 8.27, X.51,9.30, 9.152, 9.75,10.00,10.28, 10.67, 14.40pm. solution was concentrated in vacuo, and the residue was chromatographed on a 20 X 20 cm X 2 mm silica gel plate (E. Merck AG And. Caicd for ( : 2 : $ l 2 , 3 0 2 : (7, 82.10; H, 8.39. Found: C, 82.11; H, 8.3ti. Darmstadt; GF-254). The diol band was collected eluting with 5% ether-hexane and recrystallized from ethanol t,o give 411 mg (82%) 1,2-Diphenyl-3- tert-butyl-4,4-dimethyl-2,3-cyclopentanediol. of the pure diol: mp 163-164 "C; NMR (CDC13) 7 9.29 (s, 9 H , t-Bu), T o a stirred ether (20 mL) suspension under nitrogen of 300 mg (12.5
1502 J . Org. Cliem., Vol. 43, No. 8, 1978
Zimmerman and Aasen
ether and water. The aqueous phase was extracted with ether, and 8.85 (broads, 6 H, CH3), 7.47-8.19 (AB q, 2 H, J = 14 Hz, CHz), 7.00 the ether extract was washed with water and saturated aqueous so(broads, 1 H, OH), 6.35 (s, 1H, CH), 6.05 (broads, 1H, OH), 2.32-3.16 dium chloride. The dried ether solution was concentrated in vacuo, (m, 10 H, aromatic);IR (CHC13) 2.71-3.18,3.23, 3.25,3.32,3.47,6.24, and the residue was recrystallized from hexane. The product (4.68 g, 6.32, 6.69, 6.74, 6.81, 6.91, 7.16, 7.22,7.29, 7.56,7.73,8.03,8.45,8.88, 90%) was a 1:1 mixture of diastereomers. In subsequent reactions the 8.98,9.23,9.42,9.55,9.71,9.97,10.20,10.47,10.98,11.20,11.29,11.90, mixture or either isomer was used successfully. The isomers were 14.16 pm. separated by fractional recrystallization from hexane. Isomer with Anal. Calcd for C23H3002: C, 81.61; H , 8.93. Found: C, 81.39; H, mp 184-185 O C : NMR (CDC13) T 9.00 (s, 9 H , t-Bu), 6.40 (d, 1H, J = 8.83. 11 Hz, CH (Y to carboxyl), 5.89 (d, 1 H, J = 11Hz, CH p to carboxyl), 1,2-Diphenyl-3-tert-butyl-5,5-dimethylcyclopentadiene. A solution of 390 mg (1.15 mmol) of l-tert-butyl-2,3-diphenyl-4,4- 2.72-3.24 (m, 10 H, aromatic),2.02 (broads, 1H, COOH); IR (CHC13) 2.68-3.18,3.23,3.25, 3.29, 3.31,3.34, 3.37,3.42, 3.46,5.83,6.25,6.33, dimethyl-1,2-cyclopentanedioland 1.80 mL (19.5 mmol) of phos6.69,6.74,6.87, 7.16, 7.30, 7.55,7.78, 7.90,8.38,8.51, 8.81,9.01,9.23, phorous oxychloride in 10 mL of dry pyridine was refluxed for 18 h. 11.90, 12.35,14.06,14.22 9.32,9.64,9.83,9.96, 10.44,10.87,11.17,11.49, After cooling, the reaction mixture was poured into saturated aqueous ammonium chloride, and the aqueous phase was extracted with ether. w. Isomer with mp 200-202 "C: NMR (CDCl3) T 9.38 (s, 9 H, t-Bu), The combined extract was washed with saturated aqueous sodium 6.81 (d, 1H, J = 11Hz, CH CY to carboxyl), 5.88 (d, 1H, J = 11Hz, CH bicarbonate, water, and saturated aqueous sodium chloride. The ether p to carboxyl), 2.36-3.12 (m, 10 H, aromatic), 1.60 (broad s, 1 H, solution was dried and concentrated in vacuo. The residue was COOH). chromatographed on a 20 X 20 cm X 2 mm silica gel plate (E. Merck Anal. (mp 184-185 "C isomer) Calcd for C19Hz202: C, 80.81; H, 7.86. AG Darmstadt; GF-254). The fastest moving band was collected and Found: C, 80.56; H, 7.72. recrystallized from ethanol to give 276 mg (73.9%) of the cyclopen2-Phenyl-3- tert-butyl-1-indanone. A solution of 6.10 g (21.6 tadiene: mp 119-122.5 "C; NMR (CDC13) T 8.93 (s, 9 H, t-Bu), 8.80 acid mmol) of the mixture of 2,3-diphenyl-4,4-dimethylpentanoic (s, 6 H , CH3's), 3.97 (s, 1H, vinyl), 2.44-3.08 (m, 10 H, aromatic); IR isomers and 2 mL of thionyl chloride in 150 mL of dry benzene was (CCld) 3.23, 3.25, 3.29, 3.36, 3.40, 3.43, 3.48,6.25,6.69,6.73,6.76,6.83, refluxed for 1h. After cooling, 2.93 g (22.0 mmol) of anhydrous alu6.93,7.18,7.33,7.37,7.49,7.79,8.08,8.31,8.53,9.06,9.30,9.71,10.42, minum chloride was added in small portions. The resulting solution 271 nm (c 10.68, 10.94, 13.7ti, 14.12, 14.20 pm; UV (EtOH) ,A, was refluxed for 1h. The solution was cooled and poured into cold 5% 7400). hydrochloric acid. The aqueous phase was extracted with ether, and Anal. Calcd for C23H26: C, 91.33; H, 8.67. Found: C, 91.05; H, the extract was washed with water and saturated aqueous sodium 8.67. chloride. The ether-benzene solution was dried over anhydrous 2,3-Diphenyl-4,4-dimethyl-3-hydroxypentanoic Acid. Under magnesium sulfate and concentrated in vacuo to give an oil which Ivanov condition^.^^ an ether (150 mL) solution of 375 mmol of isocrystallized on standing. Recrystallization from hexane gave the pure propylmagnesium bromide was added dropwise with stirring under indanone (3.80 g, 66.7%)as a colorless solid: mp 115-117.5 "C; NMR nitrogen to a solution of 20.4 g (150 mmol) of phenylacetic acid in 150 (CDC13) T 9.00 (s, 9 H, t-Bu), 6.68 (d, 1 H, J = 1.5 Hz, CHI, 6.21 (d, mL of anhydrous ether. The solution was stirred a t room temperature 1H, J = 1.5 Hz, CH), 2.08-3.00 (m, 9 H, aromatic); IR (CHC13) 3.24, overnight. To this was added a solution of 22.1 g (136 mmol) of pi3.26,3.30, 3.33,3.38, 3.40, 3.44, 3.49, 5.88,6.25, 6.33,6.71,6.78,6.82, valophenone in 150 mL of anhydrous ether over 75 min. The mixture 6.85,6.90, 7.18,7.32, 7.46, 7.55, 7.62, 7.75,7.86,8.16-8.26, 8.54,8.71, was stirred a t reflux for 4 h and then for 18 h a t room temperature. 9.10, 9.18,9.32, 9.66,9.86, 10.10, 10.47, 10.70, 11.04, 11.31, 11.60, 11.75, The reaction mixture was hydrolyzed by the addition of 250 mL of 14.39 pm. 5% hydrochloric acid followed by the addition of 200 mL of water. The Anal. Calcd for C19Hzo0: C, 86.31; H, 7.63. Found: C. 86.36: H, aqueous solution was extracted with ether, and the extract was washed 7.60. with water and saturated sodium chloride. The ether solution was 1- tert-Butyl-2-phenyl-3-cyanoindene. Following the general dried over anhydrous magnesium sulfate and concentrated in vacuo. procedure of Evans,*O a mixture,of 2.30 g (8.39 mmol) of 2-phenylThe crude product was recrystallized from ether-hexane to give 33.3 3-tert-butyl-l-indanone, 3 mg of anhydrous zinc iodide, and 3 mL of g (82%) of the hydroxy acid as a 4:l mixture of diastereomers. The trimethylsilyl cyanide under nitrogen was stirred at room temperature diastereomers were partially separated by fractional recrystallization overnight. The reaction mixture was diluted with ether and washed from ether-hexane: NMR major isomer (CDC13) T 9.32 (s,9 H, t-Bu), with water. The ether solution was dried and concentrated in vacuo 5.40 (s, 1 H , CH), 2.21-3.20 (m, 12 H , aromatic, OH, and COOH); to give an oil which was analyzed (NMR) as a 1:l mixture of the deNMR minor isomer (CDCl3) 7 9.04 (s, 9 H, t-Bu), 5.41 (s, 1 H, CH), sired cyanohydrin trimethylsilyl ethers. 2.21-3.20 (m, 1 2 IT,aromatic, OH, and COOH); IR mixture (CHC13) Without further purification, the product was dissolved in 25 mL 2.70-3.13, 3.23, 3.26, 3.31, 3.34, 3.37, 3.42, 3.47, 5.83,6.25,6.69,6.74, of 3:l ( v h ) methanol-water containing 300 mg (5.56 mmol) of am6.87, 7.16, 7.31, 7 . 5 5 , 7.78, 7.89, 8.39, 8.52,8.81,9.24,9.33,9.64,9.82, monium chloride. The solution was stirred a t room temperature for 9.97, 10.45, 10.89, 11.20, 14.06, 14.22pm. 4 h before diluting with water and extracting with ether. The comAnal. Calcd for C19H2:!03: C, 76.47; H, 7.44. Found: C, 76.27; H, bined ether extract was washed with water and dried over anhydrous 7.39. magnesium sulfate. The solution was filtered and concentrated in 3,4-Diphenyl-4- tert- butyloxetan-2-one. The general procedure vacuo to give the cyanohydrins as a light yellow oil. of Adam38 was used A solution of 11.9 g (40.0 mmol) of 2,3-dipheThe crude cyanohydrins were dissolved in 12 mL of dry pyridine nyl-4,4-dimethyl-.3-hydroxypentanoic acid (the mixture of diastecontaining 2.34 g (15.2 mmol) of phosphorous oxychloride. The soreomers) and 10 mL (78.5 mmol) of benzenesulfonyl chloride in 200 lution was refluxed for l h. Upon cooling to room temperature, the mL of dry pyridine was stirred for 4 h a t room temperature under solution was poured into cold 5% aqueous hydrochloric acid. The nitrogen. The reaction mixture was poured into 400 mL of cold 5% aqueous phase was extracted with ether, and the extract was washed hydrochloric acid and extracted with ether. The combined extract was with water and saturated aqueous sodium chloride. The solution was washed with cold 5% hydrochloric acid, water, and saturated aqueous dried and concentrated in vacuo to give 1.92 g of the crude cyanoinsodium chloride. The solution was dried over anhydrous magnesium dene. The crude product was percolated through a 2.5 X 25 cm silica sulfate and concentrated i n vacuo to give 9.54 g (84.8%)of a mixture gel column eluting with hexane. Recrystallization of the product from of diastereomeric lactones. The mixture of diastereomers was used pentane gave 1.34 g (56.5%,based on starting indanone) of pure colin subsequent transformations. The major isomer was separated by orless solid: mp 72-75 "C; NMR (CDC13) T 9.18 ( s , 9 H, t-Bu), 6.04 (s, fractional recrystallization from ether-hexane: mp 107-110 "C; NMR 1 H, CH), 2.41-3.03 (m, 9 H, t-Bu); IR (CHC13) 3.26,3.34,3.35,3.36, (CDC13) r 9.12 (s, 9 H , t - b u ) , 4.81 (s, 1 H, CH), 2.21-3.02 (m, 10 H, aromatic); IR (CHCls) 3.23,3.25,3.32,3.34,3.43,3.47,5.46,6.23,6.68,3.38,3.40, 4.48,6.76,6.83, 6.92, 7.15, 7.30, 7.55, 7.87, 8.68, 8.78,9.05, 6.83, 6.86, 6.90, 7.15. 7.30, 7.91, 8.22, 8.51, 8.64,8.70,9.40,9.66,9.74, 9.22, 9.61, 9.71, 10.15, 10.64, 10.99, 11.49, 11.88, 12.66-13.79, 14.33 9.90,9.95, 10.18, 10.42, 10.53,10.91, 11.33,11.60, 11.76,13.79,14.18, pm. Anal. Calcd for CzoH19N: C, 87.86; H, 7.01. Found: C, 87.99; H, 14.93, 16.10 pm. 7.14. Anal. Calcd for C19H2,)02:C, 81.38; H, 7.20. Found: C, 81.35; H, 7.26. 1-tert-Butyl-2-phenyl-3-formylindene. The general procedure 2,3-Diphenyl-4,4-dimethylpentanoic Acid. T o a solution of 360 of Marshal141was employed. To a solution of 590 mg (2.16 mmol) of mg (51.0 mg-atom) of lithium in 150 mL of dry liquid ammonia under 1-tert-butyl-2-phenyl-3-cyanoindenein 50 mL of dry hexane under nitrogen was added 5.20 g (17.9 mmol) of 3,4-diphenyl-4-tert-bunitrogen a t -60 "C was added 1.8 mL of a 1.40 M hexane solution of tyloxetan-2-one ( a mixture of diastereomers) in 25 mL of anhydrous diisobutylaluminum hydride. After stirring for 15 min, the solution ether.39After stirring for 1.5 h a t reflux, the reaction was quenched was allowed to warm to room temperature and stirring was continued for 2 h. The reaction was quenched by adding 15 mL of saturated by the addition of .3.50 g (65.4mmol) of solid ammonium chloride. The ammonia was evaporated, and the residue was partitioned between aqueous ammonium chloride followed by 10 mL of 5% aqueous hy-
Vinylcyclopropene Photochemistry
J . Org. Chem., Vol. 43, No. 8, 1978 1503
20 cm X 2 mm silica gel plate (E. Merck AG Darmstadt; GF-254). drochloric acid. The two-phase mixture was stirred for 15 min. The After one development with hexane, the fastest moving band was aqueous phase was extracted with ether, and the ether-hexane solucollected. The material was triturated a t -78 "C (MeOH) to give, after tion was washed with water and saturated aqueous sodium chloride. recrystallization from methanol, 106 mg (26%) of 1,2-diphenyl-3The dried solution was concentrated in vacuo. The residue was disisobutenylindene. The second band contained nonhydrocarbon masolved in 10 mL D f 1:l (vlv) ether-methanol and treated with 10 mL terial (41$,)
from a-carbon-hydrogen insertion was identified through its spectral characteristics which were similar to those of 2 and through conversion of the crude reaction product to the corresponding acid in 30% yield. The structure of the acid was confirmed by spectral analysis. The T H T system, similar to the T H F system, did not yield products resulting from insertion into either the P-carbon-hydrogen bonds or the carbon-sulfur bond.6 Olefinic products were observed in small amounts by NMR spectroscopy, but their structures were not determined. Product analysis was performed after nitrogen evolution had ceased even though mercury formation was not complete at that time (Table I). Photolysis of 1 in Pyrrolidine. Three products were isolated from the photolysis of 1 in pyrrolidine. The major product, 4, was isolated in 48%yield. The structure of 4 was determined from spectral properties and from sodium borohydride reduction7 to ethyl a-(N-pyrro1idino)acetate( 5 ) .A
I
I
C02Et
C0,Et 4
I
i
COlEt 5
0022-326317811943-1506$01.00/0 0 1978 American Chemical Society
H
