One-Pot Synthesis of 3-Aryl-3H,4H-[1,2]-dithiolo[3,4-b]benzothiopyran-4-ones and 1-(o-Bromophenyl)-3-aryl-2-prop-2-en-1-ones

3-Aryl-3H,4H-[1,2]dithiolo[3,4-b]benzothiopyran-4-ones were prepared by the reaction of 1 equiv. of 2'-bromoacetophenone with 3.5 equiv. of potassium O-ethyl xanthate and 1 equiv. of an appropriate aromatic or heteroaromatic aldehyde. The yields of the thiopyran-4-ones are high. The key step of the reaction appears to be the conversion of the aldehyde to the corresponding thioaldehyde by the xanthate. The thioaldehyde is subsequently trapped by the anion of 2-thioxothiochroman-4-one intermediate. The intermediacy of thioaldehydes was confirmed by treating aldehydes with potassium ethyl xanthate in the absence of 2'-bromo ketones. Additionally, chalcones were readily prepared by the condensation of 2'-bromo ketones with appropriate aldehydes in the presence of potassium O-ethyl xanthate.