PREPARATIVE AND MECHANISTIC INVESTIGATIONS OF SELECTED SULFUR CUMULENES

Abstract

The key intermediates for all subsequent work ofthis thesis were the 2,2-dialkylchroman• 4-ones 190. The methodology for their preparation is well documented, ie. the reaction of2• hydroxyacetophenone with the appropriate ketone in the presence of base (pyrrolidine). Compounds 190a-d were treated with thionyl chloride at room temperature overnight to give yellow crystals of a-chloro p-monooxo sulfenyl chlorides 191a-d? Derivatization ofsulfenyJ chlorides with simple thiols such as thioacetic acid, thiobenzoic acid and thiophenol are uncomplicated to give the unsymmetrical disulfides 192a-j and 193. The substitution ofthe sulfenyl chlorides 191 with cyanide ions takes a straightforward cause with formation of the thiocyanates 194a,c,d which apparently are undisposed to rearrangement to the corresponding isothiocyanates 218. The latter would have been interesting derivatives of the often elusive a-halo amines. As on ultimate proof an X-ray structure determinati on of 194a was performed. When methoxide ions were employed as nucleophile vis-~• vis 191 we obtained the sulfenyl acid methyl esters 195a,c corresponding to anaJogous observations. The alternative sulfoxide structure for 195a,c (as a consequence of ionization• recombination rearrangement of 195) could be excluded by spectroscopic arguments, i.e. the 'H and 'C NMR resonances of the O-methy! group of the ester are compared with those of, say, methanol and dimethyl sulfoxide. .Sulfinate when reacting with the sulfenyl chlorides 191a-d gives concomitant substitution and reduction (with fonnation ofthe corresponding sulfonyl chloride as coproduct). This means that the treatment of 191a-d with sulfinate ions revealed the operation of two competing reactions, straightforward nucleophilic substitution at sulfenyl sulfur, i.e. formation of 196, and reduction to 197a-d with subsequent dimerization to the Diels-Alder dimer 198a-d. Phosphine and iodide ions only effect reduction ofour sulfenyl chlorides to give the Diels• Alder dimers 198 (with formation of iodine and triphenylphosphine oxide as coproduct,

respectively).