Nazarov cyclization of 4-cycloalkylidene-5-(trimethylsilyl)pent-1-en-3-one derivatives. Synthesis of spiro[4.5]decane, spiro[4.4]nonane, and their derivatives

ASpiro[4.5]decane and spiro[4.4]nonane ring systems were synthesized by FeCl3-induced Nazarov cyclization of alpha-(trimethylsilylmethyl)divinyl ketone derivatives. It was found that the double bond position of the product is controlled by the presence/absence of alpha'-substituent, while trimethylsilyl group is essential to obtain the products in good yields. Spiro[4.4]nonanes having exo-methylene group underwent rearrangement to bicyclo[4.3.0]nonanes. (C) 2000 Elsevier Science Ltd. All rights reserved.