Reformatsky samarium-mediated

A substoichiometric protocol for Reformatsky-type addition of a-halo esters, a-halo ketones, a-halonitriles, and a-halophosphonates to carbonyl compounds has been developed via samarium-mediated reaction.150 p-Hydroxy esters and P-hydroxynitriles have been obtained in good to excellent yields. 

Zinc versus Samarium Mediated Reformatsky Reactions... 

A Rh-catalyzed Reformatsky reaction of chiral imine (24) led to the stereoselective preparation of the a,a-difluoro-jS-amino acid (25). 25 was converted to difluor-oalkene (26), and subsequently L-Val-i/r[(Z)CF=CH]Gly derivative (23) in greater than 82% for both steps. The samarium diiodide-mediated reductive transformation of the y,y-difluoro-a, S-enoates proceeded via successive two-electron transfers to form a dienolate species which upon kinetically controlled trapping with fert-BuOH formed 23 (Scheme 6). 

The more than 125-year-old Reformatsky reaction of aldehydes or ketones with a-haloesters is a valuable alternative to the aldol reaction leading also to P-hydroxycarboxylic esters [158]. In its classic version, the reaction occurs through zinc enolates, but not only zinc can serve as a mediator but also various other metals in low oxidation stage like titanium, indium, and samarium. In... 

Guided by the success of the Evans and related auxiliaries, several attempts were made to use enantiomerically pure a-bromoacyl oxazolidinones for stereoselective Reformatsky reactions. Fukuzawa and coworkers developed the reaction of various bromoacetyl oxazolidinones 323 as an alternative to an asymmetric acetate aldol addition. The conversion was mediated by samarium iodide and yielded P-hydroxy carbonyl compounds 325 with high diastereoselectivity in optimal combinations of auxiliary group and aldehyde. Among the different auxiliaries, the geminal dimethyl- and diphenyl-substituted ones performed better than the original Evans oxazolidinones. The stereochemical outcome was rationalized by assuming that an O-bound samarium(III) enolate reacts via a chair-like... 

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