Tetracyclic condensed thiophenes, synthesis

The Hinsberg reaction has been used in two cases to prepare tetracyclic condensed thiophenes from 1,2-diketones and thiodiglycolic esters.68 One example is shown in Scheme 7 for the synthesis of 29 (13% overall).43,69 If water is not added during the process, one isolates the half-ester (27% for methyl half-ester of 207), which undergoes decarboxylation with copper... 

Synthesis, of tetracyclic and penlacyclic condensed thiophene systems. 32, 127 Synthesis and reactions of l-azirines. 13, 45 Synthesis of heleroeycles through nucleophilic additions to acetylenic esters, 19, 279... 

In 1951-1953 Rabindran and Tilak51,52 introduced a new dibenzo-thiophene synthesis and extended it to tetracyclic and pentacyclic systems. This method involves a two-step process of condensing a thioarenol with an a-halo ketone or a-haloacetal to form an a-(arylthio) ketone or a-(arylthio)-acetal intermediate, which is subsequently cyclized intramolecularly. The three principal variations introduced by Tilak and co-workers are presented in Schemes 3, 5, and 6 and were summarized in I960.528... 

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