Tandem Cycloaddition Chemistry: Part I. Synthesis and Crystallographic Analysis of 1-Azafenestranes. Part II. Synthesis and Reactivity of N-Vinyl Nitrones
Montgomery, Justin
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https://hdl.handle.net/2142/84229
Description
Title
Tandem Cycloaddition Chemistry: Part I. Synthesis and Crystallographic Analysis of 1-Azafenestranes. Part II. Synthesis and Reactivity of N-Vinyl Nitrones
Author(s)
Montgomery, Justin
Issue Date
2006
Doctoral Committee Chair(s)
Denmark, Scott E.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
Tandem cycloaddition chemistry has been explored with regard to the synthesis and crystallographic analysis of molecules of theoretical interest, the 1-azafenestranes, and the development of a new type of heterodiene, the N-vinyl nitrone. The tandem [4+2]/[3+2] cycloaddition of a nitrocyclopentene was applied as the key step in the synthesis of c,c,c,c-[5.5.5.4]-1-azafenestrane·BH 3, which was completed in only 5 steps and 26% overall yield from 1-nitrocyclopentene. This azafenestrane was analyzed crystallographically as its BF3 adduct, and significant distortion of the bond angles (120° and 121°) of the central carbon was observed. A minor product from the key [4+2] cycloaddition reaction was converted to a more strained analogue, t,c,c,c-[5.5.5.4]-1-azafenstrane·BH 3, which displayed deviation from tetrahedral geometry of 16.8° for the N-C-C central angle and is the most strained azafenestrane completed to date. During the course of synthesis of these azafenestranes, an unexpected dyotropic rearrangement was discovered that converts nitroso acetals into tetracyclic aminals. Through conformational analysis, a means to suppress the rearrangement was hypothesized and later realized experimentally through the use of a modified vinyl ether in the [4+2] cycloaddition reaction. A general synthesis of N-vinyl nitrones through selenoxide elimination was developed. Beginning from nitroalkenes, conjugate addition of benzeneselenol provides 2-nitro selenides which can be reduced to the corresponding hydroxylamines and combined with benzaldehyde to provide N-vinyl nitrone precursors. Oxidation and elimination gives a number of variably substituted N-vinyl nitrones. Three X-ray crystal structures of N-vinyl nitrones were obtained and the first intramolecular [4+2] cycloaddition of this heterodiene was documented. Computational analysis provided insight into the mechanism of the cycloaddition.
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