Azodicarboxylates and Azodicarboxamides

The reactions of electrophilic animation displayed little if any stereoselectivity (Table 3.10, entries 1 to 6). The chromatographic separation of the diastereomers was generally quite difficult. The menthyl and bomyl carbamate moieties in products 99a and 99b proved to be very stable and difficult to remove, even with prolonged reflux in 6 M HC1 or concentrated HBr, and the corresponding a-hydrazino acids could not be obtained in reasonable yield. However, the isobomyl 99c analogues were readily hydrolyzed. 

In both cases, only one diastereomer could be detected using high-temperature H NMR spectroscopy. Removal of the oxazolidinone auxiliary from compounds (S,S)-101 and (/ ,R)-101 by treatment with lithium hydroperoxide followed by acidification and treatment with diazomethane generated the corresponding methyl esters (S)-102 and (/ )-102 which have opposite configuration at C2. Amination of either 

In conclusion, the geometry of the Evans enolate completely controls the diaster-eoselection, and the effect of the isobomyl moieties is solely to increase steric bulk and enhance the ratio. 

Macrocyclic azodicarboxylates containing a steroid skeleton were also synthe-tized using a similar synthetic route [52]. These compounds were trapped by Diels-Alder reaction with cyclopentadiene. 

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