A mixture of 2-(di-tert-butylphosphino)biphenyl and dicarbonylacetonato rhodium(I) provides an effective catalyst system for the addition of alkynes to aldehydes and activated ketones. In contrast to the more common zinc-catalyzed processes, enolizable 1,2-dicarbonyls are excellent substrates for these rhodium-catalyzed additions. This reaction allows for the formation of propargylic alcohols under mild conditions, tolerating many functional groups (such as carboxylic acids) that are incompatible with other methods. Little selectivity was observed in cases of unsymmetrical 1,2-diketones. Addition of alkynes to aldehydes with an adjacent chirality center usually provides the Felkin addition product with excellent selectivity in some cases. Studies on the catalyst structure show that both the beta-diketonate and a carbon monoxide ligand appear to be bound to the active catalyst. The use of chiral phosphines to induce asymmetry in the propargyl alcohol products provided low enantioselectivity, which may be due to the phosphine having a distal relationship to the reacting centers. Modification of other ligands, such as the beta-diketonate, appears to be a more promising avenue for the development of an enantioselective variant.

[reaction: see text] The rhodium-catalyzed addition of alkynes to 1,2-diketones, 1,2-ketoesters, and aldehydes provides a method for the synthesis of tertiary alkynyl alcohols under mild conditions. The reaction tolerates many functional groups (such as carboxylic acids) that are incompatible with other methods. The alkyne addition reaction proceeds best using bulky phosphine ligands such as 2-(di-tert-butylphosphino)biphenyl. This method fills a void in the more common zinc-catalyzed processes, which give poor yields with enolizable 1,2-dicarbonyl substrates.

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Alkynes Q 0087Addition of Alkynes to Aldehydes and Activated Ketones Catalyzed by Rhodium-Phosphine Complexes. -The catalyst shown in the scheme efficiently promotes the addition of a number of alkynes to aldehydes and activated ketones. Various functional groups are tolerated. The reaction of some chiral aldehydes proceeds with high stereoselectivity. Preliminary tests concerning an asymmetric version are disappointing. -(DHONDI, P. K.; CARBERRY, P.; CHOI, L. B.; CHISHOLM*, J. S.; J. Org. Chem. 72 (2007) 25, 9590-9596; Dep. Chem., Syracuse Univ., Syracuse, NY 13244, USA; Eng.) -Jannicke 16-070