Fluoride Ion-Promotedα-Ketol Rearrangement during Unmasking of Silyl-Protected Medium-Ring Dihydroxy Ketones
作者:Ryan E. Hartung、David G. Hilmey、Leo A. Paquette
DOI:10.1002/adsc.200404002
日期:2004.6
A new strategy for implementing α-ketol rearrangements under mild conditions is presented. The reactants are mono- and disilylated stereoisomers of α,α′- and α,β-dihydroxycycloheptanones and -cyclooctanones. Compounds of this class experience ready deprotection upon treatment with tetrabutylammonium fluoride. In certain examples, this process is accompanied by structural isomerization. Since the product
The reaction of g.-halo ketones (alpha-iodocycloalkanones, alpha-bromocycloalkanones, alpha-iodo-beta-alkoxy esters, and alpha-iodoacyclic-ketones) with irradiation under a high-pressure mercury lamp gave the corresponding alpha-hydroxyketones in good yields. For alpha-bromoketones, it was found that alpha-hydroxylation does not occur. However, alpha-bromoketones were convened into a-hydroxyketones in the presence of KI. In the case of alpha,alpha(1)-diiodo ketones, alpha,alpha(1)-dihydroxyketones, which up to now have scarcely been reported, were obtained. This reaction affords a new, clean and convenient synthetic method for alpha-hydroxy- and alpha,alpha(1)-dihydroxyketones. (C) 2005 Elsevier Ltd. All rights reserved.
Reactions of α,α‘-Dihydroxy Ketones with Phosgene. Structural Requirements for Spiro Epoxy Carbonate Formation
作者:Leo A. Paquette、Ryan E. Hartung、John E. Hofferberth、Judith C. Gallucci
DOI:10.1021/ol036497+
日期:2004.3.1
[reaction: see text] Apha,alpha'-dihydroxy ketones having two OH groups that can come into close proximity react with phosgene in the presence of DMAP to produce 1,3-dioxane-2,5-diones. When covalent bonding in this manner is prohibited, alternate reaction pathways can in principle be adopted. Of these, the generation of spiro epoxy carbonates is shown to be feasible in three examples. In other cases
Synthesis of Stereoisomeric Medium-Ring α,α‘-Dihydroxy Cycloalkanones
作者:Leo A. Paquette、Ryan E. Hartung、John E. Hofferberth、Ivan Vilotijevic、Jiong Yang
DOI:10.1021/jo0358675
日期:2004.4.1
The stereochemical course of the epoxidation of the silyl enolethers of 2-tert-butyldimethylsilyloxycycloheptanone and -cyclooctanone has been investigated and shown to proceed exclusively anti to the existing α-substituent. 2-(Benzyloxy)cyclooctanone behaves similarly, and the presence of a transannular double bond does not alter the outcome. α-Ketol rearrangements are seen to operate during ensuing