Ketene-S,S-acetals as 1,3-dipolarophiles towards azides. A new synthetic entry into cyclic amino acids
摘要:
Intramolecular azide cycloaddition reactions of ketene-S,S-acetals proceed to give a reactive imine as the initially-formed intermediate and this mechanism is supported by thermolysis of (18) which gave the stable imine (22). N-Acylation of this intermediate leads to cyclic variants of 2-amino ketene-S,S-acetals (20, 24, 27), which can be viewed as masked alpha-amino acids, and reduction leads to the corresponding dithiane (21, 25, 29a). Both systems have been converted to cyclic alpha-amino acids and the scope, in terms of the ring sizes available, and the limitations of this intramolecular cycloaddition process are discussed.
Parallel Kinetic Resolution of Racemic Aldehydes by Use of Asymmetric Horner−Wadsworth−Emmons Reactions
作者:Torben M. Pedersen、Jakob F. Jensen、Rikke E. Humble、Tobias Rein、David Tanner、Kerstin Bodmann、Oliver Reiser
DOI:10.1021/ol991387h
日期:2000.2.1
[reaction: see text] A racemicaldehyde can undergo parallel kinetic resolution (PKR) by simultaneous reaction with two different chiral phosphonates, differing either in the structure of the chiral auxiliary or in the structure of the phosphoryl group (i.e., one (E)- and one (Z)-selective reagent). This strategy allows conversion of a racemicaldehyde to two different, synthetically useful chiral
[(BINAP)Re(O)Cl3] as an efficient catalyst for olefination of chiral α-substituted aliphatic aldehydes
作者:Daniel Strand、Tobias Rein
DOI:10.1016/j.jorganchem.2010.06.008
日期:2010.9
A convenient one-pot preparation of [(BINAP)Re(O)Cl3] (6) is described. This complex was demonstrated to be an efficient catalyst for the olefination of aldehydes by reaction with α-diazo esters, with essentially quantitative yields and up to 98:2 geometric selectivity. The potential for using enantiopure [(BINAP)Re(O)Cl3] (6) to promote an asymmetric kinetic resolution of racemic α-stereogenic aldehydes
Kinetic resolutions of the racemicaldehydes 3a-c by reaction with chiral phosphonopropionates 2 have been studied. Reagent 2d gives (Z)-alkene products in good yields and diastereoselectivities from all three substrates.
Henry reactions of nitroalkanes call be initiated with diethylzine in the presence of catalytic amounts of 1,2aminoethanol or 1,2-diaminoethane. (C) 2002 Elsevier Science Ltd. All rights reserved.
New Approaches towards the Synthesis of Alkenes using the Horner-Wadsworth-Emmons (HWE) Reaction as the Key Step