2-vinylcyclopropane-1,1 -dicarboxylate

A photochemical route to racemic estrone commencing with 2-bromo-5-methoxytoluene depended upon the generation of a quinodimethane intermediate incorporating an enolic component (ref. 129). Subsequently the method was adapted to furnish an asymmetric synthesis of (+)-estrone as described in the ensuing section. The cyclopentanone component was derived by the reaction of dimethyl malonate with E-1,4-dibromobut-2-ene to give racemic dimethyl 2-vinylcyclopropane-1,1-dicarboxylate which was then transformed by reaction with dimetyl methylmalonate followed by hydrolysis into racerruc 2-methyl-3-vinylcyclopentanone. 

Figure 1.38 Rh-catalyzed alkenylation reactions (a) 3-phenylpyrazole with H2C=CHR (R = Ph, COjMe) [92] and (b) N-methoxybenzamide with dimethyl-2-vinylcyclopropane-1,1-dicarboxylate [93].

The intermediacy of >/2-cyclopropene complexes of nickel has been proposed in catalyzed 2+1 reactions of free cyclopropene with electron-poor olefins, to give vinylcyclo-propanes. For example, the reaction of fumarate esters with 3,3-disubstituted cyclopropenes in the presence of Ni(COD)2 catalyst gave vinyl-substituted trans-2,3-cyclopropane dicarboxylate esters (equation 235)72 302. However, when maleic esters were used instead, a mixture of both cis and trans vinylcyclopropane diesters is obtained. 

Z)-2-butenylene dicarbonate with dimethyl malonate gives a low yield (20—40%) of 2-vinylcyclopropane-l,l-dicarboxylate with up to 70% ee (Scheme 2-38) [54], Reaction with methyl acetoacetate or acetylacetone takes place in a different manner to give a dihydrofuran derivative (59% ee), which results from nucleophilic attack of enolate oxygen at the cyclization step, (c) Asymmetric elimination of an acetyl-acetate ester gives (R)-4-rerr-butyl-l-vinylcyclohexene of up to 44% ee (Scheme 2-39) [55]. (d) Palladium-catalyzed allylic silylation is also applied to asymmetric synthesis... 

Treatment of ethyl 2-vinylcyclopropane-l,l-dicarboxylate (528) with diethyl sodiomal-onate gives mainly the tetraester 582 which arises almost exclusively from the 1,5 mode of opening together with minor amounts of the tetraester 583 resulting from a 1,7-opening. 

Elimination of methanesulfonate has been used in the synthesis of optically active dimethyl (5)-2-vinylcyclopropane-l,l-dicarboxylate (9). l,8-Diazabicyclo[5.4.0]undec-7-ene with a catalytic amount of 4-(dimethylamino)pyridine was used to effect elimination of the mesylate in nearly 50% yield. Other methods of obtaining vinylcyclopropane 9, including direct dehydration of the alcohol with the Burgess reagent, were unsuccessful. 

The reaction of diethyl sodiomalonate with diethyl 2-vinylcyclopropane-l,l-dicarboxylate (6) led to a 5 1 mixture of the 1,5- and 1,7-adducts 7 and 8 when performed in 1,2-dimethoxy-ethane. In ethanol as solvent, the formation of additional products was observed. Spiro-activated vinylcyclopropanes gave exclusively the 1,5-addition products. ... 

Dimethyl 2-vinylcyclopropane-l,l-dicarboxylate reacted with the anion generated from dimethyl methylmalonate via the 1,5-addition product to give a cyclopentanone derivative 10. ... 

In a similar fashion, diethyl cyclopropane-1,1-dicarboxylate (4) reacted with lithium dialkyl-cuprate to give the corresponding malonates S in high yields. Byproducts could be formed by the attack of the organometallic reagent at the carbonyl function. With diethyl 2-vinyl-cyclopropane-1,1-dicarboxylate (6), a preference for the 1,7-addition of the dialkylcuprate was found. Similar observations were made with 1-acetyl- (9,R = Me) and 1-benzoyl-2-vinylcyclopropane (9, R = Ph) when reacted with various dialkyl- and diphenylcuprates and with a vinylcyclopropanedicarboxylate fragment incorporated into a polycyclic system to yield compound 11. ... 

The stabilized carbanion that is formed as an intermediate in the addition of the cuprate reagent to diethyl 2-vinylcyclopropane-l,l-dicarboxylate (6) can be alkylated by various alkyl halides prior to workup. A number of different disubstituted malonates 12 were obtained by this procedure. 

In a synthesis of optically active 11-deoxy-PGEi, Abraham [141] prepared the cyclopropane derivative (133) by ozonolysis of the methyl ester of (-)-2-vinylcyclopropane-l,l-dicarboxylic acid and elaboration of the resulting aldehyde, and then effected a condensation with trimethyl heptane-1,1,7-tri-carboxylate to give, after hydrolysis, the cyclopentanone (134) which afforded 1 l-deoxy-PGE and its C-IS epimers on alkali treatment. 

Equimolar quantities of -cyclopropylstyrene and maleic anhydride in dry benzene refluxed 48 hrs. 4-phenylcyclohept-4-ene-l,2-dicarboxylic anhydride. Y 40%.— Activated vinylcyclopropanes act as a conjugated system. S. Sarel and E. Breuer, Am. Soc. 81, 6522 (1959). 

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