Cleavage of a chiral auxiliary using RCM on an especially sterically crowded alkene: Syntheses of chiral carbo- and heterocycles
摘要:
Chiral 1,5-, 1,6-, and 1,7-dienes generated in 3-4 steps from chiral auxiliary p-menthane-3-carboxaldehyde undergo RCM with notable discrepancies in reactivity depending on the nature and number of substituents flanking the central double bond. The chiral auxiliary is thus cleaved releasing a carbo- or heterocycle in the process. Special features concerning the RCM on these especially crowded systems are discussed. (c) 2006 Elsevier B.V. All rights reserved.
Initiated, tert-butyl hydroperoxide-loaded, low-temperature autoxidation of alkenes: a chemoselective synthesis of allylic hydroperoxides, allowing analysis of the regioselectivity of hydrogen atom abstraction from some unsymmetrically substituted substrates
作者:John L. Courtneidge、Melanie Bush
DOI:10.1039/p19920001531
日期:——
A method for the preparation of allylic hydroperoxides is introduced: the method involves the rapid, low-temperature, initiated autoxidation of an alkene (in these instances 1-methylcyclohexene and the isomeric 4-methyloct-4-enes) in the presence of tert-butyl hydroperoxide. The success of the method relies upon the selectivity of hydrogen atom abstraction from the substrate by the chain-carrying tert-butylperoxyl
The key THF derivative (9a) for an enantioselective synthesis of amphidinolideX/Y was obtained from 1a via a selenoetherification reaction. In fact, among the cyclization methods investigated, the highest yield and stereocontrol were achieved at -78 degrees C with PhSeCl/EtiPr2N from diols 1a (anti-Z) and 1b (anti-E) and with PhSeCl/ZnBr2 from diols 1c (syn-Z) and 1d (syn-E). Also, surprisingly, use