Search

The self-association and tautomerism of (E)-isatin-3-4-phenyl(semicarbazone) and (E)-N-methylisatin-3-4-phenyl(semicarbazone) were investigated in solvents of various polarity. In weakly interacting non-polar solvents, such as CHCl3 and benzene, phenylsemicarbazone concentrations above 1×10−5 mol dm−3 result in the formation of dimers or higher aggregates of E-isomers and . This aggregate formation prevents room temperature E–Z isomerization of and to more stable Z-isomers. In contrast to the situation in non-polar solvents, E–Z isomerization from the monomeric form of phenylsemicarbazone and E-isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70 °C. Moreover, decrease in phenylsemicarbazone concentration below 1×10−4 mol dm−3 in these highly solute–solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results. Copyright © 2013 John Wiley & Sons, Ltd.

Vinylsulfoxyallenes (3a-c) are prepared from propargylic alcohols in 47-65% yield. Vinylsulfoxyallenes undergo facile [4+2] cycloadditions with methyl triazolidenedione (MTAD) and singlet oxygen to afford phe- nylsulfinylpyridazines and spirocyclic phenylsulfinyl-2H-pyran-3(6H)- ones in excellent yields (60-90%). Spirocyclic phenylsulfinyl-2H-py- ran-3(6H)-ones are oxidized to the corresponding phenylsulfones with peracid or can be epoxidized with basic hydrogen peroxide. Spirocyclic pyranone formation is thought to proceed via the rearrangement of a labile cyclic peroxide intermediate (14)