Part I. The Stereochemistry of Carbanions Formed by Base Catalyzed Decomposition of Azoacetates
Although the stereochemical capabilities of carbonium ions have been extensively investigated, the stereochemical fate of carbanions has been subjected relatively little to systematic scrutiny. The fact that only a limited number of clean-cut sources of carbanions are available has added difficulty to such investigations.
The stereochemical capabilities of carbanions has been extensively and thoroughly examined in recent years by Cram and coworkers. However, the carbanion carbon developed in the reactions employed was bonded in every case to an unsaturated (usually aromatic) group. No fully aliphatic carbanion has been subjected to such a stereochemical study.
The reaction of lead tetraacetate with ketohydrazones to form azoacetates has been reported recently by Iffland, Schafer and Salisbury (1). The base catalyzed decomposition of an azoacetate provides a simple way to produce carbanions under mild reaction conditions.
Thus, a potentially advantageous approach is available to develop dissymmetric carbanions from azoacetates having a dissymmetric alkyl group bonded to the azo nitrogen atom. Furthermore, a successful approach to the formation of the necessary optically active azoacetates has been demonstrated (2). The carbanion of special interest is the methylethyl-n-propyl methyl anion, since this represents one of the simplest potentially dissymmetric fully aliphatic carbanions. For convenience, this ion and the related alkyl group will hereafter be designated as the t-heptyl anion or t-heptyl group.
A number of base catalyzed decomposition reactions of azoacetates which provide information about the stereochemical capabilities of the t-heptyl anion have been investigated and are described in Part I of this dissertation.
The necessary azoacetates were ultimately prepared from resolved t-heptylamine. The determination of the optical purity of the t-heptylamine was desired and its measurement was attempted unsuccessfully by the method of nmr analysis of diastereomeric amide derivatives. Suitable derivatives have been prepared from the acid chloride of O-methylmandelic acid in related situations. However, this led to the discovery of an anomalous decarbonylation reaction of α-substituted carboxylic acids when treated with thionyl chloride. The examination of this reaction is reported in Part II.