Alkene Diamination, enantioselective

Several catalysts that can effect enantioselective epoxidation of unfunctionalized alkenes have been developed, most notably manganese complexes of diimines derived from salicylaldehyde and chiral diamines (salens).62... 

Brunner, Leitner and others have reported the enantioselective transfer hydrogenation of alpha-, beta-unsaturated alkenes of the acrylate type [50]. The catalysts are usually rhodium phosphine-based and the reductant is formic acid or salts. The rates of reduction of alkenes using rhodium and iridium diamine complexes is modest [87]. An example of this reaction is shown in Figure 35.8. Williams has shown the transfer hydrogenation of alkenes such as indene and styrene using IPA [88]. 

Enantioselective osmylotion of alkenes. Osmium tetroxide forms a 1 1 wine-red complex with the chiral diamine l2 that effects efficient enantioselective dihy-droxylation of monosubstituted, oww-disubstituted, and trisubstituted alkenes (83-99% ee) at -110° in THF. The enantioface differentiation in all cases corresponds to that observed with t/mr-3-hexene and the complex with (-)-l. Essentially complete asymmetric induction is observed with frans-l-phenylpropene (99% ee). 

A first example of an enantioselective catalytic diamination of alkenes has been developed, which employs enantiopure titanium complexes as catalysts and bis(r- butylimido)dioxoosmium(VIII) as the nitrogen source.129... 

Experimental observations of the aziridination of styrene-type alkenes, catalyzed by CuPF6 in the presence of chiral diimine ligands (such as (lR,2R,A i4A i4)-A A -bis(2,6-dichlorobenzylidene)cyclohexane-l,2-diamine 425), have been taken as evidence of the intermediacy of a discrete, monomeric Cu(lll)-nitrene complex, (diimine)Cu=NTs 423. Variation of the steric properties of the aryl group in the oxidant TsN=IAr (Ar = Ph, 2-/-Bu, 5,6-Me3C6H) has no effect on the enantioselectivities in forming the aziridination products 424 (Scheme 108) <1995JA5889>. 

Chiral Mn salen complexes have been prepared by replacing ethylenediatnine with a chiral diamine such as 1,2-cyclohexanediamine, and these complexes show very high enantioselectivity in the epoxidation of alkenes, especially cyclic ones. The Mn-catalyzed asymmetric epoxidation of alkenes is known as the Jacobsen or Jacobsen-Katsuki epoxidation. 

Using the catalytic base (12.18), Duhamel and coworkers have demonstrated that elimination of HBr from substrate (12.19) can be achieved with remarkable enantioselectivity in the formation of the alkene (12.20), while diamine (12.21) has been used as a highly enantioselective base catalyst in the rearrangement of... 

As seen in Scheme 2.21, a reasonably high enantioselectivity can be obtained with sterically hindered substrates, whereas simple alkenes gave significantly lower ees. Interestingly, products of opposite stereochemistry were obtained in the epoxidation of trans-stilbene using the two different (S, S) -diamine ligands shown in Scheme 2.21. 

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