Synthesis and reactions of 3,3′-dibromodihydrodipyrrins

Abstract
The dibromodihydrodipyrrin diester 7 was prepared by reaction of the corresponding pyrrole 6 with dimethoxymethane and BF3·Et2O. Subsequently 7 was converted into the dibromodihydrodipyrrin 2 in moderate yield. The diformyldihydrodipyrrin 3 was readily prepared by methylenation of the pyrrole 9 with BF3·Et2O, followed by deprotection. Attempted synthesis of the porphyrin 1 from 2 and 3 was unsuccessful because of the low reactivity of 2. The reaction of 7 or 11 with hexabutylditin in the presence of a Pd catalyst produced a new type of tin complex 12 in low yield. This complex was also readily obtained by an alternative procedure and found to revert to 7 upon reaction with TFA.

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