Cyclopentene derivatives fused ring

The structure of the cyclic enone affects the stereoselectivity in the formation of the four-membered ring, as could be seen in the photoaddition of testosterone derivatives 159 and 162 to cyclopentene. Rubin and colloborators88 reported favored cis -fused product... 

Maas and co-workers have elaborated the approach to l-oxa-2-silacyclo-pentene derivatives based on cyclization of a siloxyalkylidenecarbene. Thus, as a result of intramolecular aliphatic C — H insertion of the carbene derived from diazo ketone 576, l-oxa-2-sila-4-cyclopentenes 577 were obtained in high yields. Here, the insertion may occur in primary, secondary, and tertiary C—H bonds (87CB635 94JOM115). When no C—H bond is adjacent to the Si atom, as in substrate 578, the cyclopropanation of a benzene ring with concomitant ring expansion may result in oxasilacyclopentene 579 (86CC1782). Photolysis or catalytic decomposition of bissilanes 580 furnishes fused bicyclic heterocycles 581 in moderate yields (90JOM229). 

The reaction of the bromoacetal, derived from (hydroxymethyl)cyclopentene, with tributyltin hydride affords m-fused acetals as a mixture of diastcreomers2. In the case of the unsubstituted alkene, due to the low rates for the cyclization, noncyclized reduction products are observed. Incorporation of an ester substituent accelerates ring closure to make cyclization the exclusive pathway. 

Sonawane s group, meanwhile, disclosed the photosensitized irradiation of carene-derived VCPs to [4,5]-ring-fused cyclopentenes using toluene as a photosensitizer. A variety of VCPs... 

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