Spiroannulation of a cyclopentane ring. Synthesis ofspiro[4.n](n+5)alk-2-en-1-ones

Department of Organic Chemistry, Indian Institute of Science, Bangalore-560 012, India

Manuscript received 5 August 1999

A methodology based on Claiscn rearrangement-Wacker oxidation and intramolecular aldol condensation strategy starting from cyclic ketones leading to spiro[4.n](n+5)alk-2-en-1-ones has been developed. Thus one-pot Claisen rearrangement of the allyl alcohols 6a-c furnished the aldehydes 8a-c, which on regiospecific oxidation using Wacker conditions generated the keto-aldehydes 9a-c. Finally, intramolecular aldol condensation transformed the keto-aldehydes 9a-c into spiroannulated products 10a-c.