Synthesis of scopin acetate and 6,7-didehydrohyoscyamin. Intramolecular phenylsulfenylation of a nonactivated methylene group of ethyl N-demethyl-3-O-(phenylthio)tropine-N-carboxylate
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The synthesis of scopin acetate (6b) and 6,7-didehydrohyoscyamine (17) was achieved by using tropine (5) as the starting compound. Formal (phenylthio)-radical transfer to the nonactivated 6-position of ethyl N-demethyl-3-O-(phenylthio)tropine-N-carboxylate (9) by irradiation in the presence of hexabutyldistannane is a key step of this synthetic approach, involving ethyl 6,7-didehydro-N-demethyltropine-N-carboxylate (15) as a synthetic intermediate (Schemes 3 and 5). The reaction of 9 with tributylstannane in the presence of ethyl acrylate, as a radicophilic olefin. involves Michael-type alkylation at C(6) of the tropine skeleton affording ethyl N-demethyl-N-(ethoxycarbonyl)tropine-6-propanoate (18) (Scheme 6).
Source:Helvetica Chimica Acta, 2003, 86, 9, 3179-3186
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