Vinylamines, reduction

Vinylamines (enamines) are reduced by alane, mono- and dichloroalane to saturated amines, and hydrogenolyzed to amines and alkenes [710]. Reduction is favored by dichloroalane while hydrogenolysis is favored by alane. Alane, chloroalane and dichloroalane gave the following results with -N-pyrrolidinylcyclohexene V-pyrrolidinylcyclohexane in 13, 15 and 22% yield, and pyrrolidine and cyclohexene in 80, 75 and 75% yields, respectively [710]. Saturated amines were also obtained by treatment of enamines with sodium borohydride [711], with sodium cyanoborohydride [103, 712] (Procedure 22, p. 210) and by heating for 1-2 hours at 50-70° with 87% or 9S% formic acid (yields 37-89%) [320]. 

In order to study the shape of a polymer chelate, viscometric measurements of a homogeneous solution of PVP were carried out46. The reduction in viscosity of the PVP solution with increasing concentration of metal ions is shown in Fig. 8(a). At constant PVP concentration, an increase in the amount of metal ions added causes a decrease in viscosity, which reveals that the polymer-ligand chain is markedly contracted due to intra-polymer chelation. An intra-polymer chelate takes a very compact form and the metal ions are crowded within the contracted polymer chain, as illustrated in Fig. 8(b). The contracted shape of an intra-polymer chelate was also reported for PAA47, poly(vinylamine)48, and poly(vinylalcohol)49. ... 

Whether these radicals serve as electron donors (to yield iminium cations) or as hydrogen atom donors (to yield vinylamines) will depend on the nature of the reaction partner, particularly on its reduction potential. In any case, the quantum yield of C N cleavage reactions are low, since they require several consecutive processes, i.e. successive transfer of an electron, a proton, and a second electron, or a mechanistic equivalent thereof. 

The present methods for the preparation of N acyl a arylenamides include (i) reductive acylation of ketoximes with iron metal [2] or phosphines [3] in the presence of acyl chlorides or acyl anhydrides (Method A) (ii) metal catalyzed coupling of vinyl halides [4], triflates [5], or tosylates [6] with amides (Method B) (iii) reaction of imine intermediates derived from nitriles with acyl chlorides or anhydrides (Method C) [7] and(iv) Pd catalyzed coupling ofaryl tosylates with N acyl vinylamines (MethodD) [8]. 

The products are J3,4.tetrahydropyridines and piperidinesii04 and sometimes cyclohexenones formed by ring opening of l,4-dihydropyridines 039,1105 If initial attack occurs at C(2), further reduction of the vinylamine linkage... 

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