LiO<i>^t</i>Bu-Promoted Intramolecular 1,3-Dipolar Cycloaddition of the 2′-Alkynyl-biaryl-2-aldehyde <i>N</i>-Tosylhydrazones Approach to 3-Substituted 1<i>H</i>-Dibenzo[<i>e</i>,<i>g</i>]indazoles

Abstract

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiOtBu-promoted intramolecular 1,3-dipolar cyclization of 2′-alkynyl-biaryl-2-aldehyde N-tosylhydrazones was developed. The N-Ts-hydrazones used were prepared in situ via the reactions of 2′-alkynyl-biaryl-2-aldehydes and TsNHNH2 (p-methylbenzenesulfonohydrazide). Two types of signals related to the hydrogen bonds, forming in several products, were observed in the 1H NMR spectra recorded in DMSO-d6, assigned to N-H bonds in their dimeric species of product and tautomer.

Keywords

• <i>N</i>-tosylhydrazones
• 1<i>H</i>-dibenzo[<i>e</i>,<i>g</i>]indazoles
• intramolecular cycloaddition
• lithium <i>tert</i>-butoxide
• hydrogen bonds