Alkenes unactivated, reductive coupling

A tremendous amount of progress has been made over the past decade in the understanding of the catalyzed reductive coupling of unactivated alkenes and alkynes. Both early and late transition metal complexes accomplish the reaction with good yields and with low catalyst loadings. Enynes and dienes can... 

Broene RD (2007) Reductive Coupling of Unactivated Alkenes and Alkynes. 279 209-248 BrogginiM (2008) Nemorubicin. 283 191-206... 

Reductive coupling of alkenes with ketones can also be carried out chemically using SmU in THF/HMPA (10 1) with added /-PrOH or /-BuOH [183]. For reduction of unactivated terminal alkenes, the yields are generally high, 70-100% [183]. 

A much more highly diastereoselective process results when alkenic 3-keto ester and 3-ketoamide substrates can be utilized in the ketone-alkene reductive coupling process. Both electron deficient and unactivated alkenes can be utilized in the reaction (equations 65 and 66). In such examples, one can take advantage of chelation to control the relative stereochemistry about the developing hydroxy and car-boxylate stereocenters. Favorable secondary orbital interactions between the developing methylene radical center and the alkyl group of the ketyl,and/or electrostatic interactions in the transition state account for stereochemical control at the third stereocenter. 

Samarium(ir) iodide in the presence of HMPA effectively promotes the intramolecular coupling of unactivated alkenic ketones by a reductive ketyl-alkene radical cyclization process (eq 25). This protocol provides a means to generate rather elaborate carbocycles through a sequencing process in which the resulting organosamarium species is trapped with various electrophiles to afford the cyclized product in high yield. ... 

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