Stereoselective base-induced conversion of naphthalenic precursors into naphthopyrans related to the aphin-derived glucoside B

Abstract

trans-5-Benzyloxy-3,4-dihydro-10-methoxy-1,3-dimethyl-1H-naphtho[2,3-c]pyran 21 and trans-3,4-dihydro-10-isopropoxy-7,9-dimethoxy-1,3-dimethyl-1H-naphtho[2,3-c]pyran 34 are formed with complete stereoselectivity by reaction of, respectively, 2-allyl-1-benzyloxy-3-(1-hydroxyethyl)-4-methoxynaphthalene 20 and the mixture of (E)- and (Z)-3-(1-hydroxyethyl)-4-isopropoxy-5,7-dimethoxy-3-prop-2-enylnaphthalene 30 and 31 with potassium tert-butoxide in dimethylformamide under nitrogen. The benzyloxy substituent of compound 21 is removed in three steps to afford trans-3,4-dihydro-10-methoxy-1,3-dimethyl-1H-naphtho[2,3-c] pyran 24. Compounds 24 and 34 are also transformed with complete stereoselectivity into the corresponding pseudoequatorial 4-alcohols 25 and 35 with potassium tert-butoxide in oxygenated dimethyl sulfoxide and dimethylformamide, respectively.