127732-73-4Relevant academic research and scientific papers
Indium-mediated asymmetric Barbier-type allylations: Additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents
Haddad, Terra D.,Hirayama, Lacie C.,Singaram, Bakthan
supporting information; experimental part, p. 642 - 649 (2010/04/29)
(Chemical Equation Presented) We report a simple, efficient, and general method for the indium-mediated enantioselective allylation of aromatic and aliphatic aldehydes and ketones under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 99%) and enantiomeric excess (up to 93%). Our method is able to tolerate various functional groups, such as esters, nitriles, and phenols. Additionally, more substituted allyl bromides, such as crotyl and cinnamyl bromide, can be used providing moderate enantioselectivity (72% and 56%, respectively) and excellent diastereoselectivity when employing cinnamyl bromide (95/5 anti/syn). However, the distereoselectivity when using crotyl bromide was poor and other functionalized allyl bromides under our method afforded low enantioselectivities for the alcohol products. In these types of indium-mediated additions, solvent plays a major role in determining the nature of the organoindium intermediate and we observed the susceptibility of some allylindium intermediates to hydrolysis in protic solvents. Under our reaction conditions using a polar aprotic solvent, we suggest that an allylindium(III) species is the active allylating intermediate. In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction.
Asymmetric Synthesis Using Tartrate Ester Modified Allylboronates. 1. Factors Influencing Stereoselectivity
Roush, William R.,Hoong, Lee K.,Palmer, Michelle A. J.,Park, Jae Chan
, p. 4109 - 4117 (2007/10/02)
A detailed study of the factors that influence the enantio- and diastereoselectivity of the reactions of tartrate allylboronate 1 with chiral and achiral aldehydes is reported.The stereoselectivity of these reactions is sensitive to variables such as reaction temperature (best results invariably are obtained at -78 deg C), solvent (toluene is best for aliphatic aldehydes; THF is preferred for aromatic aldehydes), and moisture (use of molecular sieves is recommended to maintain an anhydrous reaction environment), but not on the structure of the tartrate ester.Tartrate allylboronate 1 has been found to be exceptionally reactive compared to other, previously studied allylboronates, and even the reactions of very hindered substrates (e.g., pivalaldehyde) are complete within several hours at -78 deg C.An improved method for synthesis of 1 is described that involves the reaction of allylmagnesium bromide with (iPrO)3B followed by aqueous hydrolysis and esterification with DIPT.Yields of 1 are considerably higher (65-76percent) by using this new procedure, and the crude reagent so prepared may be used directly in allylboration experiments.A simple method for standardizing solutions of 1 is described.Finally, the absolute stereochemistry of five homoallylic alcohols (5a-e) were assigned by correlation with epoxy alcohols prepared via the Sharpless asymmetric epoxidation.The results of these correlations are in complete agreement with the stereochemical picture presented in our 1985 publication.
