•The carbonyl carbon atoms of aromatic esters were reductively carboxylated by Mg.•Under our reduction conditions, 1,2-dicarbonyl compounds can survive.•Non-substituted and meta-substituted aromatic esters can be applied.Magnesium-promoted reductive carboxylation of ethyl benzoate in the presence of chlorotrimethylsilane in N,N-dimethylformamide brought about a new carbon-carbon bond formation between the carbonyl carbon atom and carbon dioxide to give the corresponding benzoylformic acid in good yield. It is noteworthy that only ethyl benzoates with substituents at the meta-position were converted into benzoylformic acid derivatives. Moreover, no mandelic acid was detected even under the reductive conditions. This result indicates that benzoylformic acid was obtained after hydrolysis of a carboxylated intermediate, which would be alive as a stabilized structure in the reaction media.

Magnesium-promoted reductive silylation of 2- and 4-vinylpyridines with chlorotrialkylsilanes in N-methylpyrrolidinone at room temperature led to the selective formation of a variety of the corresponding β-mono-silylated compounds at the terminal carbon atom in good to excellent yields, whereas silylation of 3-vinylpyridine under the same reduction conditions failed to give a complex mixture of silylated compounds. The difference of the results between 2- or 4-vinylpyridines and 3-vinylpyridine is attributed to that of the stabilizing effect to reaction intermediates by the resonance with the nitrogen atom of pyridine.

Magnesium-promoted reductive coupling of 4-vinylpyridines and ethyl trifluoroacetate in the presence of chlorotrimethylsilane in N-methyl-2-pyrrolidone resulted in selective formation of the trifluoroacetylated compounds at the β-olefinic carbon of the pyridine ring, the electron deficient carbon in good yields. In particular, 4-vinylpyridine with an aromatic ring at the β-olefinic position of the pyridine ring gave higher yield of the trifluoroacetylated compound. The nitrogen atom of the pyridine ring may play an important role in the regioselectivity of the product.

Reductive acylation of aromatic conjugated ynones with acid chlorides in the presence of magnesium metal in N,N-dimethylformamide gave the corresponding enyne derivatives as the main compounds in moderate yields. Selective transposition of the ynone triple bond to the neighboring position was observed by allene intermediate formation. The existence of an aromatic ring of the starting material played an essential role in the reaction. Moreover, the acylation produced corresponding lactones in the presence of diacid chlorides. Final product structures were fully characterized and one product, 3,5-diphenyl-2-penten-4-yn-2-yl acetate was analyzed by single-crystal X-ray diffraction.

Mg-promoted reductive silylation of 4-phenyl-3-butyn-2-one in N,N-dimethylformamide (DMF) in the presence of chlorotrimethylsilane brought about double silylation at the β-carbon and oxygen atoms of the carbonyl group to give a multifunctionalized allene with a vinylsilane moiety and a silyl enol ether moiety. A variety of allenes can be synthesized through this simple methodology. Acid-catalyzed hydrolysis of an allene derived from the trimethylsilylation of 4-phenyl-3-butyn-2-one resulted in the formation of the corresponding benzalacetone with a trimethylsilyl group at the β-position of the carbonyl group in high yield.

Mg-Promoted reductive coupling of azulene with various α,β-unsaturated ketones in the presence of chlorotrimethylsilane in 1-methyl-2-pyrrolidinone brought about regioselective formation of the corresponding 6-substituted dihydroazulenes, which were easily oxidized to the corresponding 6-substituted azulenes by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in good yields. This new regioselective method enabled us to synthesize various 6-substituted azulenes from azulene in only two steps.

Mg-promoted reduction of benzophenones in the presence of ethyl trifluoroacetate and trimethylchlorosilane in N-methyl-2-pyrrolidinone afforded the corresponding cross-coupling products, which were easily transformed into C-trifluoroacetylated compounds of benzophenones through desilylation by tetrabutylammonium fluoride.