Pyrroles continued reduction

Here, the parallels with benzenoid counterparts continue, for these compounds have no special properties - their reactivities are those typical of benzenoid aldehydes, ketones, acids, and esters. For example, in contrast to the easy decarboxylation of a-acids observed for pyrrole and furan, thiophene-2-acids do not easily decarboxylate. Just as in benzene chemistry, Wolff-Kischner or Clemmensen reduction of ketones is a much-used route to alkylthiophenes, hypochlorite oxidation of acetylthiophenes a good route to thiophene acids, Beckmann rearrangement of thiophene oximes is a useful route to acylaminoth-iophenes and hence aminothiophenes, and esters and acids are interconvertible with no complications. 

The synthesis of calcimycin continued with oxidation of 50, reaction of the aldehyde with 24 to give 51 as a mixture of Cio-diastereomers. Treatment of this mixture with 10-camphorsulfonic acid gave 52. Presumably only the desired Cio diastereomer cyclized to the spiroacetal. The synthesis was completed by reductive cleavage of the N-N bond (pyrrole nitrogen protecting group) and hydrolysis of the trifluoroacetamide and methyl ester. 

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