New Addition Reactions of Organometal Compounds with 4,4‐Dimethyl‐1,3‐thiazole‐5(4H)‐thiones

Abstract

Dedicated to Professor H. Suschifzky on the occasion of his 80th birthday (I.XII.95) Addition reactions of organometallic reagents with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones were studied.Whereas the reactions with alkyllithium and alkyl Grignard reagents occurred in the thiophilic manner, the carbophilic addition was observed with allyllithium and ally1 Grignard reagents. A radical reaction mechanism is proposed for rationalizing these observations (Scheme 5). A radical cyclization of the prepared 5-allyl-4,5-dihydro-1,3-thiazole-5-thiol derivatives yielded 1,6-dithia-3-azaspiro[4.4]non-2-enes ( -C=S).In the reactions of 1 with organometallics, it was shown that organolithium reagents undergo thiophilic addition exclusively [ 101. In contrast, organocuprates only afforded products of carbophilic addition [ 111 [ 121. Products of carbophilic and/or thiophilic attack were obtained from the reaction of 1 with Grignard reagents, depending on the nature of the Grignard reagent and the solvent used in the reaction [lo].In this paper, we report on further results from addition reactions of organometallics with a variety of 2-alkyl-substituted 1,3-thiazole-5(4H)-thiones, in which some exceptions of the previously formulated rules were observed, and possible reaction mechanisms are discussed. Furthermore, the radical cyclization of some of the prepared 5-alkenyl-4,5-dihydro-1,3-thiazole-5(4H)-thiioles was studied.

Complexes of the Gilman Reagent with Double Bonds across the π–σ Continuum

“…We believe that a dissociative mechanism involving free Me 2 CuLi would have resulted in significant methane generation. These experiments support our proposal that an associative mechanism is involved . Theoretical studies also support this conjecture …”

“…Similarly, cis ( 2 J CC = 1.4 Hz) and trans ( 2 J CC = 17.7 Hz) couplings were observed for the complex of methyl dithio-4-trifluoromethylbenzoate with 13 CH 3 (2-thienyl)­CuLi . For the complex of 13 CS 2 with Me 2 CuLi, we measured cis coupling ( 2 J CC = 4.5 Hz) to the downfield methyl group and trans coupling ( 2 J CC = 28.8 Hz) to the upfield methyl …”

“…No C–S complex (vide infra 33 ) was observed in this case. In contrast, phenyl isothiocyanate gave transient C–N complex 31 , which rearranged to a stable C–S complex (vide infra 34 ) . Stacked 1 H NMR plots for this transformation are shown in Figure .…”

“…In 1988, Bertz, Dabbagh, and Williams reported a new kind of reaction of Gilman reagents, namely, carbophilic addition to thiocarbonyl compounds, for example, thioketones and dithioesters . The “double-barreled” carbophilic addition to dithioesters was made possible by the intermediacy of reactive mixed thiocuprates (Posner reagents) .…”

“…This reaction has found some interesting applications; however, it is included here mainly for theoretical reasons. In analogy with the Kharasch reaction, where copper salts change the regioselectivity from 1,2- to 1,4-addition, they change the regiochemistry of the reactions of Grignard and lithium reagents with thiocarbonyl compounds from thiophilic to carbophilic addition …”