[reaction: see text] A study of the role of base in the isomerization of manganese-coordinated conjugated alkynyl carbonyls to the corresponding allenyl carbonyls is described. The use of phosphine additives indicates that manganese requires a ligand prior to isomerization with amine bases. A series of amine bases were also examined for their efficacy in this isomerization reaction revealing a strong dependence on pK(a). By contrast, potassium tert-butoxide led to rapid isomerization in the absence of added manganese ligand.

[Chemical reaction: see text] We report the first examples of a Michael-Stork enamine addition to allenyl esters and ketones. Studies reveal that 2 equivalents of enamine are required for optimal yields. In the case of an allenyl methyl ketone, cyclopentyl enamine addition led to 8-oxobicyclo[3.2.1]octane formation, providing evidence for the in situ formation of an enamine intermediate following the initial Michael-Stork reaction.

Cyclopentane derivatives Q 0030Michael-Stork Addition of Cyclopentyl Enamine to Allenyl Ketones and Esters. -First examples concerning the title reaction are reported. Starting from the ketone (X), an unprecedented formation of the bicyclooctane (XII) is observed. -(SILVESTRI, M. A.; BROMFIELD, D. C.; LEPORE*, S. D.; J. Org. Chem. 70 (2005) 20, 8239-8241; Dep. Chem., Fla. Atl. Univ., Boca Raton, FL 33431, USA; Eng.) -Jannicke 06-073