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Ketones 1 were converted to α-quaternary α-vinyl ketones 2 by reaction with propargyltitanium reagents, derived from propargyl carbonates 3 and a divalent titanium reagent, followed by rearrangement of the resulting α-allenyl alcohols 4 with NBS.Leave this area blank for abstract info.

Significance: The authors describe a titanium isopropoxide/trimethylsilyl chloride/magnesium mediated McMurry coupling of aryl aldehydes to biaryl olefins at nearly room temperature. The same reagent also mediates the imino pinacol coupling of aryl aldimines to 1,2-diamines.Comment: By the addition of triethylamine, the amount of undesired 1,2-diol byproduct can be minimized. In contrast to other low-valent titanium-mediated reactions, this new method allows homogeneous reaction mixtures (except for the magnesium powder) instead of slurries of activated titanium.

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Insertion reactions O 0288Two-Step Allylic Carbon Insertion Between Ketone Carbonyl and α Carbons Giving α-Quaternary α-Vinyl Ketones. -A two-step sequence involves a highly regioselective allenylation of ketones followed by rearrangement of the resulting α-allenyl alcohols with NBS. It allows the synthesis of α-quarternary α-vinyl ketones. -(HE, J.-Q.; SHIBATA, D.; OHNO, C.; OKAMOTO*, S.; Tetrahedron Lett. 49 (2008) 47, 6724-6727; Dep. Mater. Life Chem., Kanagawa Univ., Kanagawa, Yokohama 221, Japan; Eng.) -Mais 10-041