“…The catalysts involved were mainly bronsted acids (HCl, H 2 SO 4 , H 3 PO 4 , CH 3 COOH, CF 3 COOH, CF 3 SO 3 H, p-tolunesulfonic acid etc. ), [9][10][11][12][13][14] lewis acids (BF 3 .Et 2 O, SnCl 4 , MgBr 2 .Et 2 O, TiCl 4 , LiCl, Yb(OTf) 3 , Cu(OTf) 2 , Sc(OTf) 3 , AuCl 3 /AgOTf etc.) [15][16][17][18][19][20][21][22][23] and also several miscellaneous catalysts like silica gel, [24] phosphate buffer, [25] β-cyclodextrin-SO 3 H, [26] CoFe 2 O 4 @SiO 2 -SO 3 H, [27] molecular iodine, [28] Dowex 50W-X4 acidic ion exchange resin, [29] heterogeneous acid H 3 PW 12 O 40 and 9-Borabicyclo[3.3.l]non-9yl(9-BBN) triflate [14] etc.…”