Aza Morita-Baylis-Hillman reaction asymmetric

A series of A - / - n i trobe nzenesul fony 1 imincs have been reported to undergo asymmetric aza-Morita-Baylis-Hillman reactions with methyl acrylate mediated by DABCO in the presence of chiral thiourea organocatalysts with unprecedented levels of enantioselectivity (87-99% ee), albeit only in modest yields (25 19%). Isolation of a DABCO-acrylate-imine adduct as a key intermediate, kinetic investigation, and isotopic labelling, have been employed to determine the mechanism.177... 

Asymmetric aza Morita-Baylis-Hillman reactions of N-sulfonylimines or N-sulfinimines with Michael accepters in the presence a Lewis base catalyst to give the corresponding chiral a-methylene-/ -amino compounds have been described [27]. 

According to another NMR study, the mechanism of bifunctional activation in the asymmetric aza-Morita-Baylis-Hillman reaction (Scheme 7) involves rate-limiting proton transfer (116) in the absence of added protic species155 (in consonance with the report summarized in Scheme 5144), but exhibits no autocatalysis. Addition of Brpnsted acids led to substantial rate enhancements through acceleration of the elimination step. Furthermore, it was found that phosphine catalysts, either alone or in combination with protic additives, can cause racemization of the reaction product by proton exchange at the stereogenic centre. This behaviour indicates that the spatial arrangement of a bifunctional chiral catalyst for the asymmetric aza-Morita-Baylis-Hillman reaction is crucial not only for the stereodifferentiation within the catalytic cycle but also for the prevention of subsequent racemization.155... 

Chiral Amines Derived from Asymmetric Aza Morita Baylis Hillman Reaction... 

Miller reported asymmetric aza-Morita-Baylis-Hillman reactions employing allenoate 22 as an a,p-unsaturated carbonyl component in the... 

Scheme 22.3 Asymmetric aza-Morita-Baylis-Hillman reaction catalysed by Sasai s bifunctional chiral pyridine catalyst.

Scheme 22.4 Asymmetric aza-Morita-Baylis-Hillman reaction between imine and allenoate catalysed by Miller s peptide-based pyridine catalyst.

But, Yukawa et al. used lanthanum isopropoxide/BINOL system, 128, for the catalysis of asymmetric aza-Morita-Baylis-Hillman reaction (reaction 7.28), in which the electron-deficient alkenes, 129, reacted with... 

In the same area, these authors have also investigated the efficiency of various chiral sterically congested phosphane-amide bifunctional organocatalysts with a binaphthyl scaffold in asymmetric aza-Morita-Baylis-Hillman reactions of A -sulfonated imines with activated olefins such as methyl and ethyl vinyl ketones." The corresponding aza-Morita-Baylis-Hillman adducts could be obtained in moderate to excellent yields (37-98%) and moderate to good... 

Shi, Y.-L. Shi, M. Ghiral Thiourea-Phosphine Organocatalysts in the Asymmetric Aza-Morita-Baylis-Hillman Reaction. Adv. Synth. Catal. 2007, 349,2129-2135. 

The cooperative effect of Brpnsted acid catalysts and thiourea catalysts has been noticed by the Shi group (Fig. 18) [74]. In their 2007 paper on chiral thiourea-phosphine catalyzed asymmetric aza-Morita-Baylis-Hillman reaction, Shi and co-workers described that when they used a freshly prepared 77-benzylidene-4-methylbenzenesulfonamide substrate, much lower yield and enantioselectivity of the aza-Morita-Baylis-Hillman product was obtained compared with their initial result when using a long-stored substrate. They subsequently found that the long-stored substrate contained a small amount of 4-methylbenzenesulfonamide and... 

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