The first asymmetric catalytic synthesis of syn-alk-1-ene-3,4-diols was developed; the regio-, diastereo- and enantioselective addition of 3-chloropropenyl pivaloate to aldehydes was made possible by exploiting Salen–Cr(II) species, in a catalytic version of the Nozaki–Hiyama–Kishi reaction.
3-Bromozinc Propenyl Esters: An Experimental and Theoretical Study of the Unique Stereocrossover Observed in Their Addition to Aromatic and Aliphatic Aldehydes
作者:A. Bottoni、M. Lombardo、G. P. Miscione、J. B. Pujol Algué、C. Trombini
DOI:10.1021/jo701661z
日期:2008.1.1
[GRAPHICS]We report the results of a combined experimental and theoretical study on the reaction of 3-bromopropenyl acetate in the presence of zinc with three different aldehydes (i.e., benzaldehyde, 2-methylpropanal, and cyclohexanecarboxaldehyde). A 80% de in favor of the anti product has been experimentally observed. with both saturated aldehydes, while for benzaldehyde, a 1:1 synlanti ratio has been found. DFT computations show the existence of three eta(1)-allylic organozinc complexes [gamma-(Z)-5a, gamma-(E)-5a, and alpha-5a], very close in energy. Only gamma-(Z)-5a and gamma-(E)-5a lead to the observed product. The computational investigation of the reaction of these allylic organozinc complexes with benzaldehyde and 2-methylpropanal demonstrates in both cases the existence of two competitive reaction paths leading to the syn and anti adducts, respectively. An anti preference has been found for 2-methylpropanal with both gamma-(Z)-5a and gamma-(E)-5a species (a diastereoselectivity larger than 80% is predicted), in agreement with the experiment. With benzaldehyde, while the reaction of gamma-(Z)-5a retains an anti-stereopreference (de = 70%), that involving gamma-(E)-5a is characterized by two degenerate transition states. In this case, the agreement between computations and experiments would be satisfactory under the assumption that the initial oxidative addition affords the gamma-(E)-5a zinc complex only. Additional MP2 computations have demonstrated that pi-stacking interactions can play a significant role in determining the relative energy of the transition states leading to the syn and anti products.
Indium- and Zinc-Mediated Acyloxyallylation of Protected and Unprotected Aldotetroses—Revealing a Pronounced Diastereodivergence and a Fundamental Difference in the Performance of the Mediating Metal
作者:Markus Draskovits、Christian Stanetty、Ian R. Baxendale、Marko D. Mihovilovic
DOI:10.1021/acs.joc.7b03063
日期:2018.3.2
were successfully applied to the indium and also zinc-mediated acyloxyallylation, with the latter being a first for an unprotected sugar. The investigation largely benefited from the choice of these more exotic starting materials as it allowed unambiguous identification/quantification of the hexose-products which are available as authentic reference materials. The observed diastereoselectivities indicate