Part I. Inverse electron demand Diels-Alder reactions of N-sulfonyl-2-(ethoxycarbonyl)-1-aza-1,3-butadienes: Scope and mechanistic aspects. Part II. Preparation of N-sulfonylimines: Application of a free radical rearrangement process to the reaction between oximes and sulfonyl cyanides
Abstract
A general approach to the preparation of a new class of 1-aza-1,3-butadienes, the N-sulfonyl-2-(ethoxycarbonyl)-1-aza-1,3-butadienes, is described and is based upon a Wittig reaction of a stabilized phosphorane and implementation of a subsequent room temperature, in situ, homolytic oxime O-sulfinyl $\to$ N-sulfonyl radical rearrangement. A study of the $4\pi$ participation of these electron-deficient N-sulfonyl-2-(ethoxycarbonyl)-1-aza-1,3-butadienes in intermolecular LUMO$\sb{\rm diene}$-controlled Diels-Alder reactions with electron-rich and unactivated olefins is described and demonstrates that the noncomplementary substitution of a C-2 electron-withdrawing substituent to the N-sulfonyl-1-aza-1,3-butadiene system lowers the 1-aza-1,3-butadiene $\rm E\sb{LUMO}$ and accelerates its participation in LUMO$\sb{\rm diene}$-controlled Diels-Alder reactions, enhances the endo diastereoselectivity, and maintains the expected regioselectivity. In addition, the studies demonstrate that the reactions display characteristics consistent with a concerted (4 + 2) cycloaddition reaction. To further extend the scope of the (4 + 2) cycloaddition reactions of this new class of 1-aza-1,3-butadienes, the $4\pi$ participation of N-sulfonyl-2-(ethoxycarbonyl)-1-aza-1,3-butadienes in intramolecular (4 + 2) cycloaddition reactions with unactivated dienophiles is detailed. The intramolecular (4 + 2) cycloaddition reactions of the alkene substrates with neutral terminal substitution (H and Me) provide a 1:1 mixture of cis and trans isomers. However, when a phenyl substituent is substituted at the alkene terminus, a strong endo diastereoselectivity is observed in the intramolecular (4 + 2) cycloaddition reaction to provide a single trans isomer. This latter result is consistent with the observations that exist in the intermolecular (4 + 2) cycloaddition reaction in which exclusive endo diastereoselectivity is observed with electron-donating and aryl dienophile substituents. A general preparation of N-sulfonylimines is described and is based upon the preparation and in situ rearrangement of oxime O-sulfinates employing sulfonyl cyanides as reagents. A study of the scope of this reaction employing p-toluenesulfonyl cyanide is detailed and indicates that ketone and aldehyde oximes are converted to the corresponding N-sulfonylimines in good yields.
Degree
Ph.D.
Advisors
Boger, Purdue University.
Subject Area
Organic chemistry
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