Asymmetric synthesis of stereodefined 7-(alk-1-enyl)-5,6,7,8- tetrahydronaphthalene-2-carboxylic acids and their precursors, bearing a polar group in the 8-position, by the 3-sulfonyl-1,3-oxazolidine method

Article abstract of DOI:10.1055/s-2000-7119

7-Bromo-1-(trimethylsilyloxy)-naphthalene 2 was subjected to asymmetric formylation by means of (R)-4-ethyl-2-methoxy-3-tosyl-1,3-oxazolidine (1). The enantiomerically pure 1-tetralones u-3 and l-3, bearing a masked formyl group, were elaborated diastereoselectively to achieve the title compounds 11, 13 and 23 by transformation of the l-oxo group to a tertiary methyl carbinol moiety or a hydroxymethyl group. Subsequently, the formyl group was converted to a long-chain alkene moiety and, finally, the carboxyl group was introduced via bromine-lithium exchange and carboxylation. Difficulties arose from the high dehydration tendencies of the intermediate tertiary alcohols and by facile epimerisation of the free hydroxyaldehydes. With examples for further application of similar strategies it is demonstrated how these problems could be solved.