Scope and Mechanism of the Pt-Catalyzed Enantioselective Diboration of Monosubstituted Alkenes
作者:John R. Coombs、Fredrik Haeffner、Laura T. Kliman、James P. Morken
DOI:10.1021/ja4041016
日期:2013.7.31
The Pt-catalyzed enantioselective diboration of terminal alkenes can be accomplished in an enantioselective fashion in the presence of chiral phosphonite ligands. Optimal procedures and the substrate scope of this transformation are fully investigated. Reaction progress kinetic analysis and kinetic isotope effects suggest that the stereodefining step in the catalytic cycle is olefin migratory insertion
Modular Construction of Protected 1,2/1,3-Diols, -Amino Alcohols, and -Diamines via Catalytic Asymmetric Dehydrative Allylation: An Application to Synthesis of Sphingosine
A new enantioselective catalysis has been developed for the one-step construction of methylene-bridged chiral modules of 1,2- and 1,3-OH and/or NH function(s) from δ- or λ-OH/NHBoc-substituted allylicalcohols and “H2C═O”/“H2C═NBoc”. A protonic nucleophile, either in situ-generated CH2OH or CH2NHBoc, is intramolecularly allylated to furnish eight possible 1,2- or 1,3-O,O, -O,N, -N,O, and -N,N chiral
3-Methyl-4H-[1,2,4]-oxadiazol-5-one: a versatile synthon for protecting monosubstituted acetamidines
作者:Alan E. Moormann、Jane L. Wang、Katherine E. Palmquist、Michele A. Promo、Jeffery S. Snyder、Jeffrey A. Scholten、Mark A. Massa、James A. Sikorski、R. Keith Webber
DOI:10.1016/j.tet.2004.09.030
日期:2004.11
The utilization of 3-methyl-4H-[1,2,4]-oxadiazol-5-one as a versatile protected acetamidine is demonstrated through employment in a variety of synthetic sequences. The potassium salt (2a) or the neutral form (2b) is alternatively shown to be superior for various synthetic reactions (i.e., alkylation, Michael addition, Mitsunobu) to incorporate side chains for further synthesis. The 3-methyl-4H-[1,2,4]-oxadiazol-5-one moiety was found to be stable to acid or base under non-aqueous conditions. It was also found to be stable to many reagents commonly used for organic synthesis. Despite this stability, the free acetamidine may be released by mild reduction including Lindlar hydrogenation or dissolving metal reductions. Alternatively, the hydroxyl amidine may be formed via alkaline hydrolysis. (C) 2004 Elsevier Ltd. All rights reserved.