Stereocontrolled routes to functionalized [1,8-bc]naphthopyran. A study on the total synthesis of quassinoids and tetrahydronaphthalene antibiotics
摘要:
The intramolecular Diels-Alder reactions of (4E,6E)-1-(5,6-dihydro-5-oxo-2H-pyran-2-yl)-2-methyl-4,6-octadienes have been examined with a planned synthesis of quassinoids, chlorotricholides, and mevinic acids. The intramolecular Diels-Alder reactions of 1-(5-oxo-2H-pyran-2-yl)-2-methylocta-4,6-dien-3-ones preferentially afforded products possessing a trans-ring junction. For 1-(2H-pyran-2-yl)-2-methyl-3-[(thexyklimethylsilyl)oxy]-4,6-octadienes the cyclization was controlled by the methyl at C-2 and led to cis-fused or trans-fused derivatives. The reactions were performed under thermal Lewis acid catalyzed and sonochemical conditions with no changes in the reaction selectivity and reaction yields. However, IMDA of 10b in the presence of silica gel produced a dramatic change in the course of the reaction.