5-Membered rings mercury derivatives

The mercury-induced cyclization of amidals derived from secondary homoallylic alcohols afforded only six-membered ring products 7 via a 6-exo mode. For short periods (under kinetic control) the fa-isomer was the major product, while for longer periods (under thermodynamic control) the trans-isomer was formed with very high stereoselectivity161,162. 

Two-carbon ring expansions of the five-, six,- and seven-membered rings of P-indanone, P-tetralone, and P-suberone can be achieved via a sensitized [2-1-2]-photoaddition of the trimethylsilyl enol ethers of the cyclic ketones with acrylonitrile or methyl acrylate followed by P-fragmentation of the alkoxyl radicals generated from the hypoiodites of the resulting cyclobutanols and mercury(ll) oxide-iodine, as outlined in Scheme 72. The ring expansion of the cyclobutanol derived from P-indanone enol ether and acrylonitrile gave an a,P-unsaturated nitrile. 

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