![]() ![]() "Recent applications of the Shapiro reaction". The decomposition of toluene-p-sulphonylhydrazones by alkali". An alternate pathway consists of the formation of the benzylboronic acid via a zwitterionic intermediate, followed by protodeboronation of the benzylboronic acid under basic conditions, which results in the final reductive product. The diazo compound could then react with the boronic acid to produce the benzylboronic acid through a boronate intermediate. The reaction is thought to proceed through the formation of a diazo compound that is generated from a hydrazone salt. The reaction tolerates a variety of functional groups on both substrates, including aromatic, heteroaromatic, aliphatic, electron-donating and electron-withdrawing substituents, and proceeds with high yields in the presence of potassium carbonate. īarluenga and coworkers also developed metal-free reductive coupling methodology of N-tosylhydrazones with boronic acids. This process produces stereoselective olefins in similar yields compared to the process in which preformed N-tosylhydrazones are used. Moreover, Barluenga and coworkers demonstrated a one-pot three-component coupling reaction of aldehydes or ketones, tosylhydrazides, and aryl halides in which the N-tosylhydrazone is formed in situ. Using hydrazones derived from linear aldehydes resulted in exclusively trans olefins, while the stereochemical outcomes of trisubstituted olefins were dependent on the size of the substituents. Stereochemistry is an important element to consider when preparing polysubstituted olefins. Moreover, and variety of aryl halides are well tolerated as coupling partners including those bearing both electron-withdrawing and electron-donating groups, as well as π-rich and π-deficient aromatic heterocyclic compounds. The scope of the reaction is wide N-tosylhydrazones derived from aldehydes and ketones are well tolerated, which leads to both di- and trisubstituted olefins. Combined with electrophilic aryl halides, N-tosylhydrazones can be used to prepare polysubstituted olefins under Pd-catalyzed conditions without the use of often expensive, and synthetically demanding organometallic reagents. Typically, nucleophilic reagents in coupling reactions tend to be of the organometallic variety, namely organomagnesium, -zinc, -tin, -silicon, and –boron. ![]() N-tosylhydrazones as reagents for cross-coupling reactions īarluenga and coworkers developed the first example of using N-tosylhydrazones as nucleophilic partners in cross-coupling reactions. ![]()
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