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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Various Baeyer-Villiger (B-V) oxidation reactions were examined by density functional theory calculations. Proton movements in transition states (TSs) of the two key steps, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) and the migration-cleavage of O-O (TS3), were discussed. A new TS of a hydrogen-bond rearrangement in the Criegee intermediate (TS2) was found. The hydrogen-bond directionality requires a trimer of the peroxyacid molecules at the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1). At the migration-cleavage of O-O TS (TS3), also three peroxyacid molecules are needed. Elementary processes of the B-V reaction were determined by the use of the (acetone and (H-CO-OOH)n, n=3) system. The geometries of the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1) and the migration-cleavage of O-O TS (TS3) in the trimer (n=3) participating are nearly insensitive to the substituent on the peroxyacid. The directionality is satisfied in those geometries. The migration-cleavage of O-O TS (TS3) was found to be rate-determining in reactions, [Me2C=O+(H-CO-OOH)3], [Me2C=O+(F3C-CO-OOH)3], and [Me2C=O+(MCPBA)3]. In contrast, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) is rate-determining in the reaction, [Ph(Me)C=O+(H-CO-OOH)3].

Lewis acid and substituent dependency on the regioselectivity of hydrosilylation of propiolate esters 1a-c with tris(trimethylsilyl)silane (2a) was found. The reaction of methyl and ethyl propiolate esters and 2a without Lewis acid and in the presence of EtAlCl2 and Et2AlCl gave beta-silicon-substituted Z-alkenes 3 selectively. On the other hand, reaction in the presence of AlCl3 in dichloromethane gave alpha-silicon-substituted alkenes 4. In the case of trifluoroethyl propiolate ester 1c, reaction with aluminum chloride-based Lewis acids gave alpha-silicon-substituted alkenes 4 exclusively. Two competitive mechanisms, free-radical and ionic, are proposed as the source of the complementary regioselectivity displayed in these reactions. A transition state of the radical-forming step was obtained computationally. The reaction of various reactive acetylene substrates and 2a without Lewis acid and without solvent at room temperature gave beta-silicon-substituted Z-alkenes 3 selectively.