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

Add time:07/25/2019    Source:sciencedirect.com

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[6.2.1.02,7]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-di-methoxymethyl 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-methoxynaphthacene-2,12-diyl diacetate were prepared.

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