Ketones reduction, diimide

Alkene Reduction. Sulfonylhydrazides deconpose into di-imide and sulfonic acid when heated. For this reason, they have heen utilized in the reduction of unsaturated compounds. When 2,4,6-triisopropylbenzenesulfonylhydrazide (TPSH) is used, the diimide can be generated at room temperature in the presence of base to reduce mono- or disubstituted double bonds selectively in the presence of trisuhstituted alkenes (eq 15). This reduction method tolerates sensitive groups such as esters, ketones, or organocohalt complexes and has heen applied in the preparation of polymers and in the synthesis of natural products (eq 16). This reagent was not effective in the reduction of resin-hound cyclic peptides. ... 

A synthesis of the biaryl moiety and the seven-membered ring core 3.16 of allocolchicine employed a C-H activation reaction as part of the intramolecular biaryl formation (Scheme 3.19). The starting material was prepared by the acid chloride variant of the Sonogashira reaction (Section 2.8), coupling alkyne 3.17 with acid chloride 3.18. Asymmetric reduction of the ketone 3.19, protection of the alcohol and reduction of the alkyne gave the substrate 3.20 for CH activation. Diimide, generated in situ, was employed for the alkyne reduction to avoid potential problems of over reduction. C-H activation and biaryl formation was then... 

Reduction of tosylhydrazones of a,/3-unsaturated ketones gives alkenes with the double bond being located between the former carbonyl and a-carbon atoms. This reaction is believed to proceed via an initial conjugate reduction followed by decomposition of the resulting vinylhydrazine to a vinyl diimide. 

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