Selective formation of angular tricyclic compounds by ruthenium-mediated ring-rearrangement metathesis.

Unsaturated spirocyclic substrates bearing two alkenyl chains underwent ruthenium-mediated ring-rearrangement metathesis through relaying cyclohexene and cycloheptene moieties to give angularly fused tricyclics. In some instances where two products were expected, high degrees of selectivity were observed. In one instance the structural parameter leading to selectivity was very subtle; in others the transformation favoured the formation of products with a cis-fused cyclohexene moiety. An unusual transformation involving ring-opening, double-bond migration, and then ring-closing was observed.

Reactions of 1,2-bis(trimethylsilyloxy)cycloalkenes with the diethyl acetals of aldehydes.

[reaction: see text] Lewis acid-mediated reactions of 1,2-bis(trimethylsilyloxy)cyclobutene with acetals derived from a variety of aldehydes, followed by treatment with Amberlyst 15 resin in TFA, yielded 1,3-cyclopentanedione products, but reactions with 3,3-dimethyl-1,2-bis(trimethylsilyloxy)cyclobutene led to 1,2-cyclopentanediones. Reactions of 1,2-bis(trimethylsilyloxy)cyclopentene gave intermediates that did not undergo skeletal rearrangement with Amberlyst 15 resin in TFA.