SYNTHESIS AND DIELS-ALDER REACTIONS OF THIOISOBENZOFURANS

Anions prepared by deprotonation of benzofused thionolactones reacted with alkylating agents preferentially on sulfur. The resulting isobenz ofurans underwent Diels-Alder reactions with dienophiles. This chemist ry was developed as a one-pot procedure for the synthesis of bridged p recursors of polycyclic aromatic compounds. The structure of one of th e adducts, dimethyl endo-1-methylsulfanyl-8-phenyl-11-oxatricyclo[6.2. 1.0(2,7)] Undeca-2,4,6-triene-9.10-dicarboxylate 5a, was determined b y single-crystal X-ray diffraction. The versatility of this approach w as extended by lithiation of the intermediate anion whereby alkylation introduced a further substituent on the aromatic nucleus. This method ology may be appropriate for the synthesis of anti-tumour prodrugs.