Diastereoselective reactions of a simple secondary grignard reagent

Miles, William H.; Rivera, Sandra L.; Rosario, Jocelyn Del

doi:10.1016/s0040-4039(00)74117-7

Cited by 13 publications

(1 citation statement)

References 30 publications

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“…The examples of (Scheme a) are stereoselective addition reactions of Grignard reagents to chiral α-alkoxy ketones 2a. The reaction examples of (Scheme b) are additions of chiral γ-alkoxy magnesium halides to ketones . Some other examples of chiral Grignard reagents such as tetrahydroisoquinoline Grignards discovered by Seebach 16 and α-alkoxy Grignard reagents 17 were also reported.…”

Section: Resultsmentioning

confidence: 98%

A Computational Study on Addition of Grignard Reagents to Carbonyl Compounds

Yamazaki

Yamabe

2002

J. Org. Chem.

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The mechanism of stereoselective addition of Grignard reagents to carbonyl compounds has been investigated using B3LYP density functional theory calculations. The study of the reaction of methylmagnesium chloride and formaldehyde in dimethyl ether revealed a new reaction path involving carbonyl compound coordination to magnesium atoms in a dimeric Grignard reagent. The structure of the transition state for the addition step shows that an interaction between a vicinal-magnesium bonding alkyl group and C=O causes the C-C bond formation. The simplified mechanism shown by this model is in accord with the aggregation nature of Grignard reagents and their high reactivities toward carbonyl compounds. Concerted and four-centered formation of strong O-Mg and C-C bonds was suggested as a polar mechanism. When the alkyl group is bulky, C-C bond formation is blocked and the Mg-O bond formation takes precedence. A diradical is formed with the odd spins localized on the alkyl group and carbonyl moiety. Diradical formation and its recombination were suggested to be a single electron transfer (SET) process. The criteria for the concerted polar and stepwise SET processes were discussed in terms of precursor geometries and relative energies.

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Section: Resultsmentioning

confidence: 98%