Abstract
Abstract A variety of activated 5-alkenyl-2-cyclohexenones, 2-carbomethoxy-4,4-dimethyl-5-(2-propenyl)-2-cyclohexen-1-one (20), 2-carbomethoxy-4,4-dimethyl-5-(3-butenyl)-2-cyclohexen-1-one (24), 2-carbomethoxy-5-(2-propenyl)-2-cyclohexen-1-one (29), and 2-carbomethoxy-5-(3-butenyl)-2-cyclohexen-1-one (33) were synthesized and their Lewis acid mediated polyene cyclization reaction was investigated. The cyclization precursors were synthesized starting with either 4,4-dimethyl-2-cyclohexenone (for 20 and 24) or 2-cyclohexenone (for 29 and 33) via 1,4-addition, carbomethoxylation, and dehydrogenation with DDQ or PhSeCl/ H2O2. It was found that, in the presence of a variety of Lewis acids, the compounds underwent facile polyene cyclization to give the[3,3,1] bridged bicyclic product and other nonbridged bicyclic products, for example 21a, 25.