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

Spiro[4.5]decane and spiro[4.4]nonane ring systems were synthesized by FeCl3-induced Nazarov cyclization of α-(trimethylsilylmethyl)divinyl ketone derivatives. It was found that the double bond position of the product is controlled by the presence/absence of α′-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.