Microwave assisted metal-/oxidant-free cascade electrophilic sulfenylation/5-endo-dig cyclization of 2-alkynylanilines to generate diversified 3-sulfenylindoles

Sulfonyl Hydrazides in Organic Synthesis: A Review of Recent Studies

“…Furthermore, sulfonyl hydrazides could act as precursors of electrophilic RSX (X=Br, I). Thiodiazonium, thiosulfonates or disulfides were conducted as key intermediates.…”

“…The Pardasani group explored the ArSI‐mediated synthesis of 3‐sulfenylindoles under microwave irradiation (Eq. 56‐1).…”

Applications of Ethynylanilines as Substrates for Construction of Indoles and Indole‐Substituted Derivatives

“…Later in the same year Aijun Lin et al [10] have reported onepot synthesis of benzo[a]carbazole 7 (Scheme 2) from o-ethynylo-ethynylanilines 5, and diazo compounds 6 via cascade annulation/ CÀ H activation catalysed by Rh(III). [11] This reaction involves 1,4-Rhodium migration on two rings as shown in the mechanism and involvedone CÀ N and two CÀ C bond formation.. The combination of [Cp*RhCl 2 ] 2 catalyst, Cu(OAc) 2 as additive and dipolar aprotic solvent DMAC is the best choice for the product formation.…”

“…Here in this section, we are discussing the application of non-metallic reaction conditions, photocatalyst mediated light driven synthesis and microwave assisted methodologies for construction of indoles from ethynylanilines under milder reaction conditions. In this direction, Shivani Sharma et al [11] have reported microwave assisted synthesis of diversified 3-sulfenylindoles 123 (Scheme 42) via metal and oxidant free cascade electrophilic sulfenylation by 5-endo-dig cyclization of 2-alkynylanilines 121. [28] Optimization studies revealed that use of catalytic amount of iodine, stoichiometric amount of sulfonyl hydrazides and PTSA as Lewis acid in 1,4-dioxane at 110°C for microwave irradiation under minimal reaction time is best choice.…”

“…Later in 2017, Yuichiro Takeda et al [62] have reported molecular iodine catalysed cyclization of 2-alkynylanilines 124 (scheme 43) in DCM at room temperature. [11] The process involves iodocyclization and then protodeiodination of the iodocyclized intermediates at room temperature. Use of other powerful iodination reagents such as IPyBF 4, and TBAI in the iodocyclization reactions, did not show better results than molecular iodine.…”