PREPARATION AND CYCLOADDITION CHEMISTRY OF THIOCARBONYLS AND SELENOCARBONYLS DERIVED FROM REACTION OF ELEMENTAL SULFUR AND SELENIUM WITH STABILIZED ALPHA-HALO ANIONS

Reaction of diethyl chloromalonate with Cs2CO3 in the presence of elemental S8 or Se(n) generates the corresponding diethyl thioxo- or selenoxomalonates which are subsequently trapped in situ with various 1,3-dienes. Similarly, the chalcogen carbonyls can be prepared from other halogenated compounds using DBU as the base and effectively trapped in Diels-Alder fashion with 2,3-dimethyl-1,3-butadiene (Table 2).