NEW TRANSFORMATIONS INVOLVING SQUARATE ESTERS - MULTICHANNEL REARRANGEMENT OPTIONS AVAILABLE TO 2-(DIMETHOXY-METHYL)-1-CYCLOALKEN-1-YL ADDUCTS

The Vilsmeier-Haack reaction of cyclic ketones with PBr3 and DMF is an effective means for generating beta-bromo-alpha,beta-unsaturated alde hydes, which are readily transformed into their dimethyl acetals. Thes e bromides are conveniently amenable to halogen-metal exchange in the presence of tert-butyllithium. The resultant organometallic intermedia tes, when treated with an equimolar amount of diisopropyl squarate, un dergo 1,2-addition to deliver alpha-hydroxy ketone adducts that have p roven to be sensitive to different rearrangements when in the presence of silica gel or boron trifluoride etherate. Although both processes involve net ring expansion of the cyclobutene ring with loss of methan ol, the similarity stops there. In the first instance, spirocyclic dik etones are produced by 1,2-shift of either of two ring carbons. In the second, extensively conjugated lactones are generated. The behavior o f the adduct originating from a lithiated quinone bisketal has also be en scrutinized.