Pyrrole, reactions with—continued reduction

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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