Correlation Michael-adduct

Determination of the anti configuration of Michael adduct. S-methyl (2/ , 3/ )-2,3-dimethyl-5-oxohexanedithioate (4, p405) by the correlation sequence 4- 5- 6->7. A reference sample of i o-2,3-dimethyl-1,4-butanediol (7) was obtained by reduction of authentic 8 (see also p 471) 8-... 

Michael-adducts [isopulegone, (18)]." y-Shift correlations are of value in assigning hydroxy- and bromo-substituent group stereochemistry adjacent to axial methyl or gem-dimethyl groups in substituted cyclohexanes.Further n.m.r. data are reported below in the discussion on absolute configuration and optical purity, as well as in individual sections. 

The cyclobutane intermediate is not an irreversible sink for the catalyst, but remains reversibly linked to the catalytic cycle. In this mechanistic scenario, the enantioselectivity of the reaction does not depend on the difference of the activation energies for the electrophilic attack on the two diastereotopic faces of the enamine intermediate and is controlled, according to the Curtin—Hammett principle, by the relative stability and reactivity of the diastereomeric intermediates (cyclobutane and enamine of the Michael adduct) downstream in the catalytic cycle [58, 60]. A very recent detailed mechanistic study of another reaction catalyzed by diarylproUnol sdyl ethers, the a-chlorination of aldehydes by iV-chlorosuccinimide, also suggests that the stereochemical outcome of this process is not determined by the transition state of the electrophilic attack to the enamine, but instead is correlated with the relative stability and reactivity of the diastereomeric 1,2-addition products from the resulting iminium intermediate [60]. 

Michael Additions. The Cu[(5,5)-/-Bu-box] (Sbp6)2 complex catalyzes the enantioselective addition of enolsilanes to fu-maroyl imides with enantioselectivities of up to 99% ee and in good yields (up to 91%). Here, the diastereoselectivity correlates with the geometry of the nucleophile ( )-silylketene acetals preferentially deliver anti adducts (eq 16), while (Z)-silylketene acetals afford syn products (eq 17). 

A total of 897 cysteine residues on 539 proteins were reproducibly adducted and captured. Most interesting was the resulting thiol modification selectivity. Only 90 proteins and 125 peptides were modified by both electrophiles (Dennehy et al., 2006). These results are indicative of selective alkylation rather than random adduction and also selective thiol chemistry of the two electrophiles. Alkylation by the Michael acceptor, BMCC, was selective for cysteines located next to arginine or lysine residues and also indicated some structural chemical selectivity. Most interestingly, of all the proteins modified, 80% were only adducted at a single cysteine residue (Dennehy et al., 2006). Results also correlated with previously suspected sites known to be susceptible to alkylation. The study by Liebler et al. (2008) represented the first global... 

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