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The ability to incorporate alkyl, alkenyl, aryl, and heteroatomic groups into substrates for the silicon-directed Nuzurou cyclization and their subsequent reactions has been investigated. In general, most of the groups are compatible with the conditions for the cyclization and do not interfere even when directly attached to the divinyl ketone. The influence of substituents on the rate of the cyclization has been addressed and is consistent with a simple mechanistic picture. 0and N-Containing functions are tolerated except when attached to the a -vinyl C-atom of the divinyl ketone. The diastereoface-directing effect of a fused cyclobutane is discussed.

Reactions, of various vinyl dienyl ketones (see la-, li) with FeCI, give rise to P,y-unsaturated m-vinyl-cyclopentenones (see 2a+, 2i, Table 2). The reaction succeeds for vinyl dienyl ketones with substituents on either double bond. Aryl dienyl and alkyl dienyl ketones (see If-h) do not cyclize cleanly. The effects of substituents on the rate of reaction is discussed in terms of the mechanism of the rearrangement. A '3C-labeling study establishes the pathway as an unusual I-hydroxypentadienyl-cation electrocyclization to a cyclopentenyl cation which collapses via a pinacol rearrangement to the a-vinyl ketone. I98HELVETICA CHIMICA ACTA ~ Vol. 7 1 (I 988)Scheme 3

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