Thiocyanates, reductive cleavage

The pyrrolo[2,l-6]-l,3,4-thiadiazepine (167) has been prepared (68% yield) through a sequence involving thiocyanation of the acylaminopyrrole derivative (165), followed by reductive cleavage of the thiocyanate group in (166), and the cyclization of the resulting thiol intermediate in the key synthetic step (Scheme 29) <92TL9567>. 

Aldol condensation of the zinc enolate of resin-bound alkyl ester 29 with aromatic aldehyde or ketone forms a P-hydroxy ester, which upon treatment with DIBAL-H leads to simultaneous reduction and cleavage of the ester moiety from the resin to give a soluble 1,3-diol 31 [31], Parallel synthesis utilizing three ester and nine carbonyl building blocks afforded a library of 27 analogs which was screened for antioxidative efficiency using a ferric thiocyanate assay. 

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