Dirhodium(II) Tetraacetate Catalyzed (Chlorovinyl)cyclopropanation of Enol Ethers and Dienol Ethers - A Route to Donor-Substituted Vinylcyclopropanes, Ethynylcyclopropanes and Cycloheptadienes

2-Chloro- (4-Cl), 3,3-dichloro- (4-Cl₂), and 2,3,3-trichlorodiazopropene (4-Cl₃) can easily be prepared in up to 70% yield by thermal fragmentation (Bamford-Stevens reaction), at 60°C in tetrahydrofuran, of the corresponding chloroacrolein tosylhydra-zone sodium salts 3-Cl_n . Tetrahydrofuran solutions of (chlorovinyl)diazomethanes 4-Cl_n thus obtained are used for cyclopropanation reactions of a large variety of alkenes. Under dirhodium(II) tetraacetate catalysis, yields of (chlorovinyl)cyclopropanes 6-Cl_n [and of vinylcyclopropanes 6-H₃ with diazopropene (4-H₃ )] are quite good especially from enol ethers. Dienol silyl ethers, 2-trimethylsiloxy-1,3-butadiene (12) and 1-(1′-trimethylsiloxyvinyl)cyclohexene (15), react exclusively at the donor-substituted double bond, the resulting 1-siloxy-1,2-divinylcyclopropanes 13-X_n, 16-X_n readily rearrange to cycloheptadiene derivatives 14 and 17-20 respectively. 2-Alkoxy-1-(chlorovinyl)cyclopropanes such as 6o-Cl₂ , 6p-Cl₂ , 6p-Cl₃ can be transformed to synthetically valuable 2-alkoxy-1-ethynylcyclopropanes 27o,p, which are also obtained by direct ethynylcyclopropanation of enol ethers with diazopropyne (28). This latter method provides the first known access to 2-siloxy-1-ethynylcyclopropane 25m.