Reaction of 1,2-Dithiete with Alkenes and Alkynes:  Experimental and Theoretical Study

Abstract

Reactions of 3,4-bis(methoxycarbonyl)-1,2-dithiete (1) with various alkenes or alkynes formed 2,3-dihydro-1,4-dithiins or thiophenes, respectively. The reactions with alkenes were stereospecific, which indicates the concerted reaction between 1,2-bis(methoxycarbonyl)ethane-1,2-dithione (13), the valence isomer of the 1,2-dithiete, and the dienophiles. Theoretical study confirmed the reactions of 13 with alkenes and alkynes are of reverse electron demand hetero Diels-Alder type. The MO calculations showed the 1,2-dithiete 1 was 5.8 kcal mol -1 more stable than the corresponding ethane-1,2-dithione 13, and the tautomerization energy between the 1,2-dithiete and the ethane-1,2-dithione was also calculated to be 28.5 kcal mol -1 from the 1,2-dithiete, which suggests the tautomerization from 1,2-dithiete 1 to ethane-1,2-dithione 13 is possible at least at high temperature. Reaction of 3,4,7,8-tetrakis(methoxycarbonyl)-1,2,5,6-tetrathiocin (2) or (Z,Z,Z,Z)-3, 4,7,8,11,12,15,16-octakis-(methoxycarbonyl)-1,2,5,6,9,10,13,14-octathiacyclohexadeca-3,7,11,15-tetraene (3) with ethyl vinyl ether also formed the 2,3-dihydro-1,4-dithiin derivative, which is the same compound obtained by the reaction of 1,2-dithiete 1 with the ether. 1,2,5,6-Tetrathiocin 2 and 16-membered cyclic compound 3 also reacted with diphenylacetylene to give the thiophene derivative.

Diels−Alder Reactions of 4-Alkenylthiazoles: A New Approach to Thiazole Functionalization

“…In none of these reactions was it possible to detect either a betaine intermediate originating from a stepwise process or a Michael-type adduct. This experimental observation and the high levels of stereocontrol of the Diels−Alder reaction point to a concerted mechanism . However, the lower temperature required when the reactions are run in acetonitrile compared to that in toluene seems to indicate that the transition state is highly polarized.…”

Electrocyclic Ring Openings of 2-Furylcarbene and Related Carbenes: A Comparison between Pseudopericyclic and Coarctate Reactions

“…The molecular plane is the only symmetry element present in the carbene and it is preserved through a planar transition state and in the ring-opened product, 2-penten-4-ynal. Clearly the in-plane and out-of-plane electrons correlate; thus the planar, pseudopericyclic ring opening is allowed. , Furthermore, the vinylogous ring openings, having either fewer or more π-electrons would also be allowed. Finally, the first excited states (n-π*) also correlate because of the effective degeneracy of the two HOMOs of 6a .…”

Unique effects of sulfur and water on the syntheses of thiaheterocycles

“…Therefore, heterocyclic vinyl thioethers motivated great interest among organic chemists to know more about them. After the isolation of 3,4-bis(trifluoromethyl)-1,2-dithiete [3], the reactions of 1,2-dithiete derivatives [4][5][6] and their isomers [7,8] with other compounds, such as alkenes [8], alkynes [6,8,9], and oxidants [7], have been extensively studied. On the contrary, halogenated alkenes or alkynes treated with inorganic sulfides also produced desirable thiaheterocyclic compounds [10][11][12][13].…”