Ene-hydrazide from Enol Triflate for the Regioselective Fischer Indole Synthesis

Abstract

Ene-hydrazide prepared from enol triflate undergoes a Fischer indolization reaction to give the corresponding indole with complete regioselectivity. The starting enol triflate is readily accessed in regiochemically defined form from the ketone precursor via various well-established methods. This new protocol was successfully applied to the synthesis of desbromoarborescidine A, a natural β-carboline alkaloid, difficult to prepare with conventional Fischer indole synthesis.

Control of the Chemoselectivity of Metal N-Aryl Nitrene Reactivity: C–H Bond Amination versus Electrocyclization

“…Vinyl triflate s12b. 23 Method C was followed using 1.35 g of LHMDS (8.06 mmol), 0.826 g of 2-methylcyclohexanone (7.36 mmol) and 2.89 g of PhNTf 2 (8.10 mmol) in 80 mL of THF. Purification by MPLC (2:98 to 10:90 EtOAc: hexane) afforded the product as a colorless oil (1.24 g, 69%); vinyl triflate s12b was previously reported by Cho and co-workers: 23 1 H NMR (500 MHz, CDCl 3 ) δ 5.72 (dt, J = 4.…”

Catalytic Enantioselective Desymmetrizing Fischer Indolization through Dynamic Kinetic Resolution

“…Inspired by the pioneering works of Yamamoto on the Lewis acid assisted enhancement of Brønsted acidity [18] and Ishiharasa pplication of this concept to chiral phosphoric acids (Table 1), [19] we wondered whether such acatalyst with enhanced acidity would facilitate hydrazone formation and its eventual conversion to indole.T ot est this possibility,w e studied the effect of equimolar quantity of various Lewis acids with respect to II. [17] Ac ombination of 5mol % II and 5mol %ZnCl 2 [20] not only improved the yield to 41 %but also afforded the product with am uch-improved e.r. of 90.5:9.5 (entry 6).…”

Synthesis of Oxazine‐Embedded 1,1′‐Biaryl‐2,2′‐diamine via [3,3]‐Sigmatropic Rearrangement of Oxazine Diarylhydrazine

“…Such difficulties together with lack of a reliable method to the BINAM core hamper further development of BINAM‐derived chiral ligands and organocatalysts. As a part of our ongoing study on aryl hydrazides, we have envisioned the oxazine unit incorporated in the 1,1′‐biaryl‐2,2′‐diamines 2 could provide the required steric bias for effective stereocontrol. Prompted by their potentials as new chiral ligands and organocatalysts, we set out to investigate the synthesis of oxazine‐embedded 1,1′‐biaryl‐2,2′‐diamine 2 by using [3,3]‐sigmatropic rearrangement of diarylhydrazines 1 (Scheme ) 4d,k,5 …”