Chiral allylsilanes in the convergent approach to spiroketal substructures.
Item
-
Title
-
Chiral allylsilanes in the convergent approach to spiroketal substructures.
-
Identifier
-
AAI9405503
-
identifier
-
9405503
-
Creator
-
Brown, David Paul.
-
Contributor
-
Adviser: Vernon G. S. Box
-
Date
-
1993
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Chemistry, Organic | Chemistry, Pharmaceutical
-
Abstract
-
The emergence of the allylsilanes as one of the more versatile reagents in organic synthesis, has sparked new interests in their syntheses and applications. In particular, are the chiral allylsilanes whose syntheses are not only challenging, but require the use of exotic and expensive reagents. Our interests in chiral allylsilanes were kindled from our terminal objective of synthesizing spiroketal substructures having stereocenters at both of the spirocarbons.;A significant part of our investigations was therefore involved with the development of a general method for generating chiral allylsilanes from easily prepared and stable lactone precursors. The method was conceptually straightforward, involving a two-fold addition of a trimethylsilylmethylmagnesium Grignard reagent to the lactone or its derivative, followed by a thermodynamically driven Petersen-type elimination of the resulting bis(trimethylsilylmethyl) carbinol species, to give the allylsilane.;The stereoselectivity of the addition reactions of these allylsilanes with functionalized benzaldehydes were examined, by which it was clearly demonstrated that the stereo-centers adjacent to the allylsilane moiety did influence the stereochemical outcome of these reactions. Subsequent spirocyclization of the addition compounds were also observed to be influenced by stereocenters remote from the cyclization sites.;The pivalate ester group was utilized in a number of our synthetic intermediates, primarily because of its relatively low migratory aptitude. From our esterification reactions we were able to determine the relative reactivities of the hydroxyl groups of 4,6-O-benzylideneglucopyranose, one of our key starting materials, towards the acylpyridinium ion. The observed differences in reactivity towards esterification was rationalized on the basis of the relative nucleophilic activation of proton acceptor sites in the molecule.;Finally, in our efforts to develop a mild, yet facile method for the pivalate ester hydrolysis, we encountered an unusual case of O(2)-O(1) ester migration. This was possible because of the high energy, and very reactive O(1) alkoxide that was formed during the cleavage process, which readily attacked the C(2) ester function in an intra-molecular fashion.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
