SYNTHESIS OF POLYCYCLIC CYCLOBUTANE DERIVATIVES BY TANDEM INTRAMOLECULAR MICHAEL-ALDOL REACTION UNDER 2 COMPLEMENTARY CONDITIONS - TBDMSOTF-ET3N AND TMSI-(TMS)2NH

The treatment of alpha,beta-unsaturated esters having a ketone function at an appropriate position with either TBDMSOTf in the presence of Et3N or TMSI in the presence of (TMS)2NH provided, via a tandem intramolecular Michael-aldol reaction sequence, several different types of cyclobutane derivatives. The two reaction conditions were complementary. Tricyclo[4.2.1.0(3,8)]nonanes 34 and 55, tricyclo[5.1.1.0(4,8)]nonane 40,tricyclo[5.4.0.0(3,7)]undecane 51, tetracyclo[5.4.0.0(3,7).0(9,11)]undecane 45, and the bicyclo[3.2.0]heptanes 56, 57, and 58, which have structures either partially or completely similar to those of endiandric acids A (1a), B (1b), and C (2), trihydroxydecipiadiene (3), lintenone (4), italicene (5), and filifolone (6), were stereoselectively synthesized by the tandem reaction.