Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• . Keywords: E/Z isomerism; indazol-3-ylidene; mesomeric betaine; pyrazole; quinazoline; Rh complex; Introduction As a result of their biochemical and pharmacological significance, there has been a considerably growing interest in indazoles in recent years, which is reflected in several book chapters and

• standard conditions (25 °C, 1 atm) was found to be 3.4 kcal/mol [20]. Alternatively, indazolium salts 2 can be deprotonated by various bases to give indazol-3-ylidenes 3 [22]. The chemistry of indazol-3-ylidene, which is a singlet carbene, is due to the considerable donor strength of the carbene atom which

• several heterocyclic transformation products (vide infra). Finally, the synthetic potential is governed by the electrophilic properties of the iminium group of indazolium salts which result from protonation of the carbene. As a consequence, the synthetic potential of indazol-3-ylidene not only strongly