Site selectivity in the reactions of various 1,3-dipoles with (phenylsulfonyl)-1,2-propadiene

Novel regioselective synthesis of 3′H,4H-spiro[chromene-3,2′-[1,3,4]thiadiazol]-4-one containing compounds

“…Nitrilimines represent an important class of highly reactive 1,3-dipoles used intensively for cycloaddition reactions with numerous unsaturated functional groups (e.g. alkenes [6][7][8][9], alkynes [10,11], azomethines [12], allenes [13,14]) as well as heterocyclic residues [5,15].…”

Site- and Regioselectivity of Nitrile Oxide–Allene Cycloadditions: DFT-Based Semiquantitative Predictions

“…Although mechanistic evidence points to the poor site-and regioselective behavior of sulfonylallenes, there has been quite a debate on this point. 14,15 Theoretical efforts have been pursued in order to rationalize the nitrile oxide−allene behavior within the frame of FMO theory. 19 Although the nitrile oxide reaction to aminoallenes was tentatively predicted to be a simple α,β-cycloaddition, 16 it should be highlighted that the FMO model is not suitable in the case of sulfonylallenes.…”

Silver(I) salts as useful reagents in pyrazole synthesis

“…18 The choice of silver(I) carbonate in the place of more common organic bases, like triethylamine 19,20 comes from the following considerations: (i) the allene → acetylene isomerisation is suppressed in the current reaction conditions; (ii) room temperature and heterogeneous reaction medium allow a smooth generation of the nitrilimine, so minimising the degradative processes of the 1,3-dipole. From a mechanistic standpoint, it is likely that the final pyrazoles 12 and 13 would originate from the first-formed cycloadducts E and F, respectively, via 1,3-prototropic shift.…”

“…From a mechanistic standpoint, it is likely that the final pyrazoles 12 and 13 would originate from the first-formed cycloadducts E and F, respectively, via 1,3-prototropic shift. 19,21 The formation of the sulfinic ester intermediates 14 can be rationalised by invoking a [2,3]sigmatropic rearrangement of cycloadduct G via a sulfur-to-oxygen bond migration. 22 It needs to be added that, due to the HOMO-nitrilimine control of the cycloaddition, electron-rich nitrilimines (entries a-c,f) gave better results, while the cycloaddition pathway appeared impervious with electron-poor nitrilimines (entries d,e).…”