Erythro diamine adducts

The putative biradical intermediate was trapped by styrene and a-methylstyrene in 30-40 percent yields. That the reaction was not concerted was shown by the fact that cis and trans-6-methyl styrenes gave an identical mixture of threo and erythro diamine adducts (24). 

A similar situation exists with sulfur epimer 61, prepared from (E,Z)-2,4-hexadiene, which is unreactive toward phenylmagnesium bromide and gives E-erythro vicinal diamine 59 in only poor yield with methy-llithium. Inspection of the conformations of the adducts 61A and 58A indicates that the path of the attacking nucleophile in the former case is more sterically crowded than in the latter. 

Since the Diels-Alder cycloadditions used to prepare various dihy-drothiazine imines generally produced mixtures of sulfur epimers, it was desirable to find a procedure to also convert the unreactive adducts to the vicinal diamines. It was discovered that adducts 60 rearranged thermally by a novel [2,3]-sigmatropic process to afford thiadiazolidines 62 stereoselectively (Scheme 1-XV). Reduction of 62 with sodium borohy-dride yielded the -threo vicinal diamine derivative 57. Similarly, unreactive adducts 61 cleanly gave thiadiazolidines 63 on heating, which could be converted to E-erythro vicinal diamines 59. This methodology thus allows both sulfur epimers from ( , )-2,4-hexadiene to be converted to the -threo product, and the epimers from ( ,Z)-2,4-hexadiene to be used to prepare the -erythro series of compounds. 

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