Annulations cyclopentanes, 1 - cyclopropane

Cyclic p-kcio esters and )9-diketones (596) smoothly effect ring-opening of 1,1-bis(benzenesulphonyl)cyclopropane (412) under basic conditions. Reductive cleavage of the resulting sulphones (597) by lithium arylides provides routes to 598 and 599 (equation 210) The bis-benzenesulphonyl compound appears to fulfil the requirements for a propylene 1,3-dipole. The fact that the sulphones can be sequentially removed permits selective introduction of from one to three electrophiles (E) (equation 211). In the case of )5-keto esters, such versatility created a novel three carbon insertion between the ester group and the ketone or a cyclopentane annulation. ... 

Peterson alkenation cyclobutane synthesis and cyclopentane annulation via l-lithio-l-(trunethylsilyl)cyclopropane)... 

Cyclopentane Annulation. Condensation of l-lithio-l-(tri-methylsilyl)cyclopropane with ketones gives vinylcyclopropane intermediates, which upon pyrolysis undergo vinylcyclopropane rearrangement to give annulated cyclopentene derivatives (eq 5). ... 

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