Synthesis of isochromans via Fe(OTf)2-catalyzed Oxa-Pictet–Spengler cyclization

Ketones as strategic building blocks for the synthesis of natural product-inspired compounds

“…Most known variants of the oxa-Pictet-Spengler 194 reaction generally display only limited ketone scope. [195][196][197][198][199] However, Waldmann recently described a ketone-tolerant oxa-Pictet-Spengler reaction using TfOH on SiO 2 as the catalyst (Scheme 34). 200 Hydroxyethyl-derived hetaryl compounds 143 were combined with ketones to rapidly produce the oxacycles 144 at room temperature.…”

Heteropolyacid ionic liquid heterogeneously catalyzed synthesis of isochromans via oxa-Pictet–Spengler cyclization in dimethyl carbonate

“…34,35 The catalysts are used in the latter are usually Fe(OTf) 2 , Bi(OTf) 3 , SnCl 4 and other expensive Lewis acid, or HCl, TfOH and other corrosive Bronsted acid (TfOH ¼ triuoromethanesulfonic acid). 33,[36][37][38][39][40] And the solvents are toluene, benzene, dioxane and so on. [41][42][43][44][45] These methods show disadvantages such as long reaction times, high temperature, and unrecyclable catalysts.…”