SULFURIZATION OF NONENOLIZABLE DIKETONES

Sulfumation of nonenolizable diketones 1a-d by Lawesson's reagent (LR) and boron trisulfide reagent (B2S3) was investigated. Sulfurization of 1,4-diketone la with LR at 50°C in benzene affords disulfide 2 (23%) and 1.3-dithietane 4a (70%) as the main products, while that with B2S3 in refluxing toluene gives 2 (62%) as the major product. Dithietane 4a probably arises from intramolecular head-to-tail dimerization of the initially formed 1.4-dithione 7a, while disulfide 2 is the product of thermal rearrangement of 4a. Sulfurization of 1,5-diketone 1b with B2S3 affords 1,3-dithietane 4b (52%) through head-to-tail dimerization of the probable intermediate, 1.5-dithione 7b. The reaction of lb with LR affords a trithiaphosphorinane derivative 6, which probably results from [2 + 2+2] cycloaddition of 7b with thionophosphine sulfide 19, which is formed by thermal dissociation of LR. 6, when heated in refluxing toluene, undergoes cycloreversion to regenerate 19 and 7b (4b as the final product in a quantitative yield), and 19 thus formed acts as a sulfurizing agent (heating benzophenone with 6 in refluxing toluene affords thiobenzophenone in 92% yield). Sulfurization of 1,6-diketone lc with LR affords dithione 7c (42%), monothione 8c (13%), 1,2,4-trithiolane 3c (5%), and 1,3-dithietane 4c (2%), while that with B2S3 gives 7c (57%), 8c (6%), and 4c (20%). Sulfurization of 1,7-diketone Id by both reagents affords dithione 7d and monothione 8d in good yields. Only thiocarbonyls of 7d do not undergo intramolecular dimerization. © 1990, American Chemical Society. All rights reserved.