Tandem reactions asymmetric conjugate addition

Anti stereochemistry in six-membered rings Conformational control from a chiral centre in the cyclohexenone Remote stereochemical control in five-membered rings prostaglandins Regio- and stereochemical control in open chain compounds Asymmetric induction by a chiral auxiliary on the enolate Tandem Michael-Michael Reactions One Conjugate Addition Follows Another Double Michael or Diels-Alder reaction ... 

Scheme 40 Asymmetric tandem p-borylation-conjugate addition reaction...

Asymmetric synthesis of lignans may involve the use of several approaches like a tandem conjugate addition reaction, a Diels-Alder reaction or a radical carboxyarylation reaction, as mentioned above. 

Deng also successfully applied the C6 —OH catalysts 64a,b to the asymmetric tandem conjugate addition-protonation reactions of the a-cyanoketones or... 

Other fates are possible for the enolate formed in the initial conjugate addition and an obvious possibility is an aldol reaction. With an asymmetric catalyst, the combination of three simple molecules leads to one enantiomer of one diastereoisomer of the tandem Michael-aldol product14 83. The catalyst 84 is based on a BINOL A1 complex (see chapters 25, 26). It can be drawn either as a lithium salt with an aluminium cation or, better, as a lithium aryloxide with a Lewis-acidic aluminium atom. This is better because both basic ArCT and Lewis acidity are necessary for catalysis. 

As already demonstrated tra 5-dibenzylbutyrolactones are valuable as precursors for the synthesis of a wide range of lignans. For example, the keto-lactones (90) and (91), which have both been prepared by tandem conjugate addition reactions, provide key intermediates for the synthesis and asymmetric synthesis respectively of lignans of the furofuran type (scheme 30) [85,86]. 

Glucosamine-derived imines 58 were used for the synthesis of carbapenem and carbacephem antibiotics. [2 + 2] Cycloaddition with methoxyacetyl chloride provided diastereomeric S-lactams with low asymmetric induction [56]. Radical cyclization and oxidation reactions of diastereoisomer 59 led to car-bapenems 60 and 61 (Scheme 16) [57]. The same research group continued the transformation of S-lactams derived from o-glucosamine. In particular, a tandem ehmination-conjugate addition performed on 62 provided the second ring of the carbacephem, for example 63 (Scheme 17) [58]. 

Scheme 2.94 Catalytic asymmetric tandem conjugate addition-protonation reaction...

The tandem arylrhodation/conjugate addition reaction, rhodium-catalyzed asymmetric arylative cyclization of cyclohexadienone-containing meso-l,6-dienynes was efficiently developed to provide optically pure d5-hydrobenzo[f ]furans with high to excellent yields and excellent enantioselectivities (13AGE5314). 

The first Cu-catalyzed asymmetric borylative cyclization reaction between cyclohexadienone-containing 1,6-enynes and B2pin2 was established to afford an optically pure d5-hydrobenzo[l ]furan framework bearing alkenylboronate and enone substructures through a tandem process of selective P-borylation of the propargylic ether and subsequent enantioselective conjugate addition to cyclohexadienone (13JA11700). 

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