2.4- Hexadiene imines

The (co)polymerization of dienes can be a good method for the preparation of polymers with reactive vinyl groups, a method that enables the preparation of polymers possessing plural vinyl groups per polymer chain. A fluorinated bis(phenoxy-imine) Ti complex was shown by Coates and co-workers to convert 1,5-hexadiene to poly(methylene-l,3-cyclopentane-fti-3-vinyl tetramethylene), which contained multiple vinyl groups. As already discussed, Saito et al. and others revealed that bis(phenoxy-imine) Ti complexes favored secondary insertion. " This is probably responsible for the formation of 3-vinyl tetramethylene units. Likewise, the same catalyst system can form sPP-/ -poly(methylene-l,3-cyclopentane-z -3-vinyl tetramethylene) from propylene and 1,5-hexadiene. Very recently. 

The practical potential of hydrogen bonds in enamines has been investigated by several authors85 in relation to studies involving polymers. In some instances (such as polymers of 1,6-diethoxy-l,5-hexadiene-3,4-dione with aromatic and aliphatic amines), mixtures of enamino ketones and imines are obtained86. 

Weinreb and coworkers have examined some reactions of dihydrothiazine imines and have developed a new approach to vicinal diamines using these intermediates. Their method is outlined in Scheme 18. Cycloaddition of ( -2,4-hexadiene with the tosyl bis-imine gives a 1.1 1 mixture of epimeric dihydrothiazine imines (140) and (144). Subsequent transformations of these adducts took two different courses. In one, adduct (140) could be opened to allylic sulfilimine (141) which underwent a stereoselective 2,3-sigmatiopic rearrangement to sulfenamide (142) (cf. equation 54). Desulfurization of (142) yielded E)-threo vicinal sulfonamide (143). Adduct (144), which presumably exists in conformation... 

Although the Diels-Alder reactions of glyoxylate N-sulfonyl imines often show high stereoselectivity, the results are inconsistent and difficult to rationalize at this point. In the case of cyclopentadiene [Eq. (42)] [58,68] and 1,3-cyclo-hexadiene [Eq. (43)] [68] the kinetic products of cycloaddition are the carboxy-late exo isomers. With the acyclic diene 1,3-dimethylbutadiene, a mixture of exo and endo products is observed with exo predominating [Eq. (44)] [58]. 

The Weinreb group has recently developed stereoselective methodology for synthesis of unsaturated vicinal diamine derivatives from dihydrothiazine imines.49 For example, when cycloadduct 54 prepared from (E, )-2,4-hexadiene was treated with phenylmagnesium bromide followed by trimethyl phosphite, E-threo vicinal diamine 57 was formed cleanly in good yield [Ea. <27)1. 

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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