STEREOCONTROLLED ROUTES TO FUNCTIONALIZED [1,8-BC]NAPHTHOPYRAN - A STUDY ON THE TOTAL SYNTHESIS OF QUASSINOIDS AND TETRAHYDRONAPHTHALENE ANTIBIOTICS

The intramolecular Diels-Alder reactions of hydro-5-oxo-2H-pyran-2-yl) -2-methyl-4,6-octadienes have been examined with a planned synthesis o f quassinoids, chlorotricholides, and mevinic acids. The intramolecula r Diels-Alder reactions of (5-oxo-2H-pyran-2-yl)-2-methylocta-4,6-dien -3-ones preferentially afforded products possessing a trans-ring junct ion. For methyl-3-[(thexyklimethylsilyl)oxy]-4,6-octadienes the cycliz ation was controlled by the methyl at C-2 and led to cis-fused or tran s-fused derivatives. The reactions were performed under thermal Lewis acid catalyzed and sonochemical conditions with no changes in the reac tion selectivity and reaction yields. However, IMDA of 10b in the pres ence of silica gel produced a dramatic change in the course of the rea ction.