Grignard reaction asymmetric induction

The carbonyl carbon of an unsymmetrical ketone is a prochiral center reaction with a Grignard reagent 2 (R 7 R, R") can take place on either face of the carbonyl group with equal chance. The products 8a and 8b are consequently formed in equal amounts as racemic mixture, as long as no asymmetric induction becomes effective ... 

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

Sodium cuprate yielded less reduction product and less thiophilic addition product than lithium cuprate at both —50 and 0 °C. In the case of silyl thiones chiral at silicon, the reactions with organolithium derivatives and Grignard reagents produce a-silylsulfides with medium to good levels of asymmetric induction and, interestingly, the asymmetry induced at the a-carbon is retained in the subsequent desilylation431 (equation 118), the process being stereoselective. 

Asymmetric reactions of a chiral glyoxylate ester. Grignard reagents add to the glyoxylate ester (2) of ( — )-l with unusually high asymmetric induction. The chirality... 

Metals other than palladium and molybdenum can be used for allylic substitution reactions. For example, nickel in the presence of the oxazolinylferrocenylphosphine 9 provides good asymmetric induction for the reaction of a Grignard reagent with allylic electrophilic systems such as acetates.151... 

Appreciable diastereoselectivity (50%) was found in the cycloaddition with buta-1,3-diene at -78 °C and the protiodesilylation of the diastereomeric mixture of the adducts with TBAF gave dihydrothiopyran with 51% ee (Scheme 28). Similar diastereoselectivity was observed in the reaction with organo-lithium and Grignard reagents which gave a-silyl sulfides in moderate yields with medium to good levels of asymmetric induction (de = 40-76%).45 As an example, the derivative with E = D gave with protiodesilylation a-deuterio benzyl methyl sulfide with 45% ee. These results lead to the conclusion that in both cases protiodesilylation occurs stereospecifically without loss of the induced chirality (Scheme 28). 

Under forcing conditions, alkyl aryl ethers are cleaved by Grignard reagents by displacement of aryloxide [A]. Such reactions are not generally useful in synthesis, but the displacement of methoxide from positions ortho to alkoxycarbonyl [2] and oxazolinyl groups [3] has been applied to the synthesis of orffco-substituted carboxylic acids, and displacement ortho to diphenylphosphino groups has also been reported [4], The following example describes the key step in a synthesis of anthraquinones. Recently, asymmetric induction by a chiral oxazolinyl substituent has been reported [5] ... 

Asymmetric Synthesis Using Grignard Reagents Table 5 Asymmetric Induction by Displacement Reactions... 

Iron catalysts are very effective for the substitution of acyl chlorides [Eq. (198) 439.440] and thiol esters [Eq. (199) 376] with Grignard reagents to yield ketones. 1.4-Addition of Grignard reagents to an alkylidenemalonate derivative, as shown in Eq. (158) [182,183] was also promoted with an iron catalyst, but the degree of the asymmetric induction was inferior to that of the reaction catalyzed by nickel. 

Imines derived from benzylamine and a,3-unsaturated ketones which represent 1-azadiene systems can be isomerized to the corresponding 2-azadienes with potassium t-butoxide. Addition of r-butyl-lithium occurs smoothly to afford simple imine anions that undergo alkylation in the usual fashion. 3S The two examples provided in Scheme 17 illustrate the power of this method to provide either a,a- or a,a -substitution. On the other hand, reaction of similar 1-azadiene systems with Grignard reagents results in addition to form the imine anion directly (equation 44). This example represents one of the early contributions to asymmetric induction in this area and will be elaborated in Section 4.1.3.5. 

Displacement reactions. The alkylative C-0 bond scission induced by Grignard reagents on 1,3-oxazolidines is subject to asymmetric induction by a substituent at C-4. The method is applicable to a synthesis of (-)-dihydropinidine. 

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