Remote Substituent Effect on the Electrophilic Additions of 1,3-Dienes - Synthesis of (2r)-5-(Acetoxymethyl)-2-Acetyl-1,2,3,4-Tetrahydro-10-Methoxynaphthacene -2,12-Diyl Diacetate

The addition of one equivalent of 2-nitrobenzenesulfenyl chloride to 1-(dimethoxymethyl)-2,3,5,6-tetramethylidene-7-oxabicyclo[2.2. 1]heptane (4) is highly regioselective giving 2-(chloromethyl)-1-(dimethoxymethyl)-5,6-dimethylidene-3 -[(-2-nitrophenylthio)methyl]-7-oxabicyclo[2.2.1]hept-2-ene (9). The reaction of 2-nitrobenzene-sulfenyl chloride with 8-(dimethoxymethyl)-9,10-dimethylidene-11-oxatricyclo[6.2.1.0(2,7)]undec -2(7)-en-4-yl methyl ketone derivatives (5, (-)-6) was also regioselective giving mixtures of 1,2- rather than 1,4-adducts resulting from competitive Markovnikov and anti-Markovnikov modes of addition, the olefinic moiety the furthest from the 8-dimethoxymethyl substituent being preferred. These adducts underwent base-induced eliminations with the formation of exocyclic thio- and chlorosubstituted dienes that added to 2,3-didehydroanisole to give products resulting from highly ''ortho'' regioselective Diels-Alder additions. The regioselectivity was the same whether 2,3-didehydroanisole was generated by nitrosation of 3-methoxy- or 6-methoxy-2-aminobenzoic acid. By applying these regioselective reactions to the Diels-Alder monoadduct of 3'-oxobut-2'-en-2'-yl (1R,5S,7S)-3-ethyl-2-oxo-3-aza-6,8-dioxabicyclo[3.2.1] octane-7-carboxylate (1-acetylvinyl RADO(Et)) with 1-(dimethoxymethyl)-2,3,5,6-tetramethylidene-7-oxabicylo[2.2.1]heptane (4), enantiopure (2R)-2-acetyl-1,2,3,4-tetrahydro-10-methoxynaphthacene-2,5-diyl diacetate and (2R)-5-(acetoxymethyl)-2-acetyl-1,2,3,4-tetrahydro-10-methoxynaphthacen- 2,12-diyl diacetate were prepared.