Tris(trifluoromethanesulfonato)indium

Abstract

(A) Loh et al. have reported the In(OTf)3 catalyzed conversion of branched homoallylic alcohols to the thermodynamically preferred linear regioisomers followed by it's utilization for the construction of steroidal side chains with anti-Cram stereoselectivity. (B) Intramolecular 3,5-oxonium-ene cyclization reaction catalyzed by In(OTf)3 in dichloromethane afford both tetrahydropyran and tetrahydrofuran rings. A tandem 2-oxonia[3,3]-sigmatropic rearrangement/cyclization reaction of homoallylic alcohols with the corresponding aldehydes catalyzed by In(OTf)3 selectively afford dimethyltetrahydrofurans and methylenedimethyltetrahydro furans. (C) An atom economic and efficient synthetic construction of tetrahydropyran rings using In(OTf)3 - catalyzed self-tandem carbonyl-ene, intramolecualr (2,5)-oxonium-ene cyclization between aldehydes and methylene cyclohexane is reported. This method provides a facile assembly of tetrahydropyran units for the synthesis of natural products containing tetrahydropyran groups. (D) Facile O-H insertion reactions of α-diazoketones with aliphatic/aromatic alcohols or benzenethiol have been developed in the presence of In(OTf)3 as a catalyst. These reactions provide good yields of α-alkoxy ketones. A comparative study with other Lewis acids establishes the reactivity of indium triflate in O-H insertion reactions of α-diazoketones with no Wolf rearrangement product. (E) in(OTf)3 is found to be an effective (reusable) catalyst for one step intramolecular Diels-Alder reaction of furans in the solid state under Microwave irradiation (8-10 mins, 80-90% yields). The reaction is less effective under thermal conditions (20-30 mins, 40-45% yields) and takes several days at room temperature, and undergo retro Diels-Alder reaction when purified by distillation. It should be noted that the yield of second (83%) and even third (80%) runs are comparable to that of first run (85%). (F) At a loading as low as 0.5 mol% it can catalyse the hetero Diels-Alder reaction of Danishefsky's diene and imines. A three component coupling reaction between aldehydes, amines, and Danishefsky's diene to afford tetrahydropyridine derivatives proceeds similarly in high yields. (G) A practical synthesis of sulfonamides is achieved through this indium catalyst by the sulfamoylation of aromatics. The reaction gives consistently good results with activated aromatics across a range of sulfamoyl chlorides but isolated yields are low with deactivated substrates such as chlorobenzenes. An intramoleclar sulfamoylation is also possible. (H) This catalyst finds important applications in protection-deprotection chemistry also. In the presence of 5 mol% of this catalyst both activated and deactivated aromatic aldehydes including a sterically hindered one such as mesitaldehyde, aliphatic aldehydes and cinnamaldehyde react rapidly with 2-mercaptoethanol (1.5 equiv) in dichloromethane as the solvent at 15°C to afford the corresponding 1,3-oxathiolanes in good to excellent yields.