Trisyl hydrazone

Methylenecycloalkanes. The vinyl anion (a) generated from the trisyl hydrazone (1) of an lo-chloroalkyl methyl ketone with jec-butyllithium (2 equiv.) and TMEDA... 

The issue of stereoselectivity of alkene formation from acyclic tosyl- or trisyl-hydrazones has been addressed in only a few cases. For straight chain ketones, there is a preference for m-alkene formation (see Scheme 67). A few other examples appear to give lower ratios, which is surprising in view of several reports of highly cis selective reactions in which the vinyllithium intermediate was trapped with electrophiles.Hydrocarbon branching in the a -position degrades the stereoselectivity considerably (Scheme 67). 

A novel class of chiral indenes (verbindenes) was prepared from enantiopure verbenone by K.C. Rupert and coworkers who utilized the Shapiro reaction and the Nazarov cyciization as the key transformations. The bicyclic ketone substrate was treated with triisopropylbenzenesulfonyl hydrazide to prepare the trisyl hydrazone that was then exposed to n-BuLi. The resulting vinyllithium intermediate was reacted with various aromatic aldehydes to afford the corresponding allylic alcohols. 

An alternative to tosyl or trisyl hydrazones is the use of phenylaziridinyl hydra-zones (e.g. 42). If the protonated alkene product is desired, then the base LDA can be used as a catalyst. LDA is regenerated by reaction of the alkenyllithium species with the by-product, diisopropylamine (2.40). ... 

Formation of Hydrazones. Much of the rich chemistry exhibited by TPSH comes from its condensation products with ketones and aldehydes. Such trisyl hydrazones are typically prepared in excellent yield by mixing equimolar amounts of reagents in methanol or ethanol at room temperature with a catalytic amount of acid such as HCl and storing the reaction in the cold. The product precipitates and is filtered off. Very hindered ketones such as camphor and diisopropyl ketone require stoichiometric amounts of acid and extraordinarily hindered ketones may not condense at aU.i ... 

Bamford-Stevens and Shapiro Reactions. The Bamford-Stevens reaction is used to obtain unsaturated compounds from tosylhydrazones. A base is required to generate its monoanion, which thermally decomposes to yield the corresponding di-azo derivatives. These reactive species evolve to give an aUcene through carbenium ions in protic solvents or carbenes in aprotic solvents. The thermal decomposition of the monoanions of trisyl-hydrazones is commonly used to obtain diazoalkanes for different applications such as functionalization of solid supports, epox-idation and alkenylation of aldehydes, or the study of radicals and carbenes The functionalization of a Merrifield resin with... 

Corey and Estreicher have developed the first method for the transformation of cyclic ketones into conjugated cyclic nitro-olefins. Following conversion of the ketone into a vinylstannane via its trisyl hydrazone, the crucial step is the replacement of tin by a nitro-group at the unsaturated carbon, for which tetranitromethane in DMSO is highly effective (e.g. Scheme 36). 

Once again, new reagents for the direct conversion of aldehydes into nitriles have been reported,probably the most useful of which is the modified reductive cyanation procedure which now allows the preparation of nitriles from aldehydes with the addition of one C-atom (Scheme 20). An analogous procedure involves the reaction of potassium cyanide with the 2,4,6-tri-isopropylbenzenesulphonyl (trisyl) hydrazones of both aliphatic aldehydes and ketones (Scheme 21). 

Practically, it is important that the aryl group has no ortho hydrogen atoms as competing ortho-lithiation (chapter 7) may interfere with the reaction. The favoured aryl group is 2,4,6-tri-isopropyl-phenyl or trisyl shown in the hydrazone 36. Hydrocarbon solvents such as hexane and addition of ligands for lithium such as TMEDA allow the reaction to go with maximum efficiency. 

Enolates reacted with trisyl azide to produce a-azido keto species however, azaenolates that originated from A(A(-dimethyl hydrazones underwent an interesting [3-b2]-cycloaddition with trisyl azide followed by a cycloreversion to provide a-sulfonamidohydrazones (eq 37). ... 

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