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

A recyclable and efficient heterogeneous, green catalyst based on the synthesis of Keggin-type polyoxometalate (H 3 PMo 12 O 40 ) and vitamin B1 analogue 3-ethyl-5-(2-hydroxyethyl)-4-methylthiazol-3-ium (HEMT), i.e. , [HEMTH]H 2 [PMo 12 O 40 ] was prepared. Oxa-Pictet-Spengler cyclization of arylethanols and aldehydes were catalyzed to afford various substituted isochromans in moderate conditions with excellent yields using dimethyl carbonate (DMC) as a green solvent. Furthermore, this protocol was applicable in a gram-scale reaction, and the catalyst could be recycled eight times without significant loss of activity.