Hydrazinolysis regioselective

Regioselectivity becomes important, if unsymmetric difunctional nitrogen components are used. In such cases two different reactions of the nitrogen nucleophile with the open-chain educt may be possible, one of which must be faster than the other. Hydrazone formation, for example, occurs more readily than hydrazinoLysis of an ester. In the second example, on the other hand, the amide is formed very rapidly from the acyl chloride, and only one cyclization product is observed. 

Heterocycles can be employed as precursors for the synthesis of pyrazoles. Pyrazoles can be synthesized by three-membered ring substrates. For example, allyl amines 12 and pyrazoles 13 could be obtained by hydrazinolysis of 2-ketoaziridines 11 <06TL255>. Regioselective ring opening of 3-aryl-2-benzoyl-l,l-cyclopropanedicarbonitriles 14 with hydrazine provided a new process for the synthesis of 5-aryl-3-phenylpyrazoles 15 <06JHC495>. 

On reaction of the corresponding l-iminomethyl-l,2,5,6-tetrahydropyridine in situ alkylation was effected by deprotonation with butyllithium at — 78 °C in the presence of haloalkanes to again afford a regioisomeric mixture of 1 and 2 (n = 2). Regioselectivity in this case was much lower (about 2 1), but hydrazinolysis followed by hydrogenation in a similar manner afforded the chiral 2-alkylpiperidines with 91-96% ee. 

The reaction of the cyclic carbonate 306 with hydrazine hydrochloride and Pr 2NEt in ethanol at reflux produced the cyclic hydrazone 307 via partial, regioselective hydrazinolysis of 306 followed by intramolecular condensation of the resultant hydrazide with the unmasked hemiacetal group (Equation 51) <2005SL2607>. 

The six mono- and di-O-butyryl derivatives of 1,6-anhydro- -D-glucopyranose and the six corresponding palmitic acid esters have been prepared from the tributyrate and tripalmitate respectively, by partial methanolysis and hydrazinolysis. The experimental findings regarding the regioselectivity of the deesterification reactions were related to polar and steric effects identified by quantum-chemical calculations (PCILO). ... 

---