“…92,93 Although previously published approaches using a homogenous catalyst for preparing spiro derivatives are valuable, these catalysts suffer from some disadvantages, such as high cost, drastic separation from the reaction mixture, long-duration reaction, and high temperature. 94–99 Over recent years, various heterogenized organic polymer catalysts based on helical polymers (single-handed helical polyisocyanides), 100 polyethyleneglycols (PEG-Ni NPs, PEG-OSO 3 H), 101,102 polystyrene (PS@GO-Fe 3 O 4 ), 86 chitosan (Fe 3 O 4 @CS-SO 3 H NPs, Bmim(OH)/chitosan/C 2 H 5 OH), 103,104 cellulose (cellulose-SO 3 H, nano-cellulose-SbCl 5 , Cu 2 O@MCC, NiII(BAPTE)(NO 3 ) 2 -Cell nanocatalyst), 105–108 polyaniline (PANI/Fe 3 O 4 /CNT), 109 and collagen protein (Fe 3 O 4 @SiO 2 /ECH/IG) 110 have been used in the synthesis of spiro-fused[4 H -pyran]. Although the above-mentioned catalytic systems can be readily separated, the recycling times were low (probably due to leaching or tedious workup).…”