Stereoselective conjugate addition

The stereoselective conjugate addition of lithium (Z)-dialkenylcuprates to vinyl sulfones gives (Z)-olefms in the range of 70-80% overall yield and no ( )-isomer is detected (equation 66)56. The degree of stereoselectivity is higher than 90%. 

Potential precursors to stereoselective INOC and ISOC reactions (e.g., 195 and 196, respectively) have been prepared via stereoselective conjugate additions of several allylic alcohols (e.g., 194,X = 0) and an allylic thiol (e.g., 194,X = S) to a chiral (E)-nitro alkene (e. g., 193) that was derived from (P)-2,3-isopropylidene... 

Scheme 6.22. Non-stereoselective conjugate addition to the -chiral enoate 102.

Selective labelling of the two diastereotopic methyl groups of i-leucine (144) has enabled their fates during secondary metabolic reactions to be elucidated [66]. Moreover, in the context of protein interactions, differentiation of the leucine pro-R and pro-S methyl groups in protein NMR spectra allows molecular recognition phenomena to be studied [67]. Recently, efficient routes to both forms of Relabeled leucine, based on application of an auxiliary-controlled stereoselective conjugate addition reaction (Scheme 6.27) have been described [68]. Thus, starting... 

Chiral /3,/3-diaryIpropionic acid moieties are often found in compounds showing biological activities, such as antiarrhythmics vasodilators antidepressives " , antihistamines and controllers of cerebral insufficiency ". In the course of synthetic studies of chiral -diaryIpropionic acid derivatives, Merck researchers developed stereoselective conjugate addition of aryllithium reagents to the a,/ -unsaturated fert-butyl esters 18 bearing a chiral imidazolidine or oxazolidine auxiliary at the ortho position of an aryl group. The addition furnished chiral -diaryIpropionic acid derivatives 19 with... 

Y. Stereoselective conjugate addition of an a-sulfmyl carbanion to a,/ -unsaturated esters asymmetric synthesis of cycloalkanecarboxy-lates. Synlett 1997, 449-450. 

A strictly nucleophilic approach can also be used for an [(N) + (C=C)] protocol Thus the chiral iodo-unsaturated bicyclic lactam 89 undergoes stereoselective conjugate addition with primary amines to give the tricyclic aziridine 90, which can be subsequently transformed into the chiral 3,4-aziridinopyrrolidine 91 by reductive cleavage. Yields of up to 90% can be achieved and facial selectivity is greater than 98 2 [95TL3491],... 

A. Bemardi, Stereoselective Conjugate Addition of Enolates to a,/3-Unsaturated Carbonyl Compounds , Gazz. Chim. ltd. 1995, 125, 539-547. 

Statine was synthesised from the oxazolidine derivative 201 obtained through a stereoselective conjugate addition of an hydroxymethyl group in a basic methanolic solution. The conjugate addition proceeded faster than the dehydroxymethylation<02OL1213>. 

These results are analogous to the pioneering work of Posner, who initially developed highly stereoselective conjugate additions of carbon nucleophiles to chiral 2-(arylsulfinyl)-2-cycloalkenones.25 This methodology has been extended to include novel diastereomer differentiating radical (3-additions in which the two... 

Garrido and coworkers116 have demonstrated the use of homochiral lithium (a-methyl-benzyljbenzylamide 175 to initiate the highly stereoselective conjugate addition-cyclization of dimethyl ( , )-octa-2,5-dienoate, 174, to generate the homochiral cyclopentane derivative (—)-(lR,2R,5R,aR)-176 with complete control over the configuration of C-l and C-2 and excellent control over C-5 (Scheme 54). 

Conjugate reduction of unsaturated epoxides Reduction of 2 methyl-l,2-oxido-3-butene (I) with DIBAH in refluxing hexane results in highly stereoselective conjugate addition to give the Z alcohol (2) the E isomer (3) is a minor product. 

Stereoselective Conjugate Addition of Organoaluminium Compounds to Carbohydrate Derived N-Acyl Oxazolidinones According to Scheme 10.59 (Ref. [147,148])... 

Rueck, K, Kunz, H, Stereoselective conjugate addition of organoaluminum chlorides to a,(i-unsaturated carboxylic acid derivatives. Synthesis, 1018-1028, 1993. 

Dondoni, A, Fantin, G, Fogagnolo, M, Merino, P, Regio- and stereoselective conjugate addition of nitrogen nucleophiles to 2-alkenyl iV-methylthiazolium iodides. Synthesis of 3-epi-daunosamine and some lincosamine analogues. Tetrahedron, 46, 6167-6184, 1990 see also Ref. [97b]. 

Bernard , A. Stereoselective conjugate addition of enolates to a, 3-unsaturated carbonyl compounds. Gazz. Chim. ttal. 1995,125, 539-547. 

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