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An Umpolung Approach to the a-Functionalization of Ketones and Aldehydes
- Abstract:
The a-alkylation of N-sulfonyl hydrazones via in situ-derived azoalkenes provides an umpolung approach to ketone a-alkylation that has considerable potential with regard to catalysis and the direct incorporation of functionality not amenable to the use of enolate chemistry. The first Cu(I)-catalyzed addition of Grignard reagents to in situ-derived N-sulfonyl azoalkenes is described. This method is remarkable in its ability to deliver highly sterically hindered compounds that would be difficult or impossible to synthesize via traditional enolate chemistry.
Also, the first asymmetric organocatalytic sulfenylation of in situ-derived nitrosoalkenes leading to chiral nonracemic a-sulfenylated ketones is described. The transformation proceeds in an umpolung fashion, relative to enolate/azaenolate methods, and uses simple thiols, thereby obviating the need for elecrophilic sulfur reagents. Moreover, excellent er’s are obtained starting from a variety of a-chloro oximes, including cyclic and acyclyic systems.
Also, the addition of cuprates to a,B-epoxy tosylhydrazones is described. The additions proceed through the intermediary of 1-azo-3-alkoxy propenes. The transformation is simple and efficient and has the unusual feature of giving high syn-selectivity, which is opposite of that produced by a simple SN2-type epoxide opening reaction. This method compatible with a,B-epoxy tosylhydrazones with additional a-substitution, which provides access to aldol-like products that would be difficult to make using traditional enolate chemistry.
Ph.D. Dissertation Defense Examination Seminar
Departmental Seminar