Lewis acid mediated cyclisation of methylenecyclopropyl ketones and aldehydes

The Lewis acid mediated cyclisation of various methylenecyclopropyl ketones , ketals and aldehydes has been investigated as a new route to six- and sev en-membered rings. Cyclisation of aldehyde 6, ketal 9 and ketone 11 with Ti Cl4 gave cyclohexene products, and cyclisation of ketal 10 gave a dichloroc ycloheptene, all via nucleophilic addition of the methylenecyclopropyl pi b ond to the activated carbonyl. Cyclisation of ketone 12, however, with SnCl 4, gave a cyclopentanol 21, presumably via nucleophilic addition of a cyclo propyl sigma bond to the activated carbonyl. (C) 1999 Elsevier Science Ltd. All rights reserved.