Stevens rearrangement of a potentially aromatic thiophenium ylide: formation of 10-methoxycarbonyl-10H-benzo[3,4]cyclopenta[1,2-b]thiopyran-9-one

Abstract

The title compound (3) has been obtained by rhodium(l1) catalysed decomposition and cyclization of methoxycarbonyl[2-(2'-thienyl)benzoyl]diazomethane (2) followed by spontaneous Stevens rearrangement of the initially formed sulphur ylide (1).

The Synthetic Potential of Thiophenium Ylide Cycloadducts**

“…In the n ‐propyl case, proton transfer may occur to provide a more stable exocyclic thiophenium ylide (Path H), which may lead to secondary degradation pathways. To test this idea, a probe 9 ax was designed where the hypothesized stabilized exocyclic thiophenium ylide 20 (Figure 5, Part D) has been previously shown to undergo ring expansion via a [1,2] alkenyl shift to produce 2 H ‐thiopyrans of type 21 [37–39] . Indeed, upon heating of the probe with either MeOH or no additive, 2 H ‐thiopyran 21 was observed as the major product of the reaction.…”

“…To test this idea, a probe 9 ax was designed where the hypothesized stabilized exocyclic thiophenium ylide 20 (Figure 5, Part D) has been previously shown to undergo ring expansion via a [1,2] alkenyl shift to produce 2H-thiopyrans of type 21. [37][38][39] Indeed, upon heating of the probe with either MeOH or no additive, 2H-thiopyran 21 was observed as the major product of the reaction. In line with the effect of AcOH-d 4 observed in the study described in Part B, when the probe 9 ax was heated in the presence of a stoichiometric amount of AcOH, only the thiophene 10 c was observed, along with a stoichiometric amount of acetate substitution by-product 19.…”

The Synthetic Potential of Thiophenium Ylide Cycloadducts

“…To test this idea, a probe 9ax was designed where the hypothesized stabilized exocyclic thiophenium ylide 20 (Figure 6, Part D) has been previously shown to undergo ring expansion via a [1,2] alkenyl shift to produce 2Hthiopyrans of type 21. [35][36][37] Indeed, upon heating of the probe with either MeOH or no additive, 2H-thiopyran 21 was observed as the major product of the reaction. In line with the effect of AcOH-d4 observed in the study described in Part B, when the probe 9ax was heated in the presence of a stoichiometric amount of AcOH, only the thiophene 10c was observed, along with a stoichiometric amount of acetate substitution by-product 19.…”

Sulfur ylides in the synthesis of heterocyclic and carbocyclic compounds

“…Thus intramolecular cyclisation of diazosulfide 8 afforded not only the major reaction product 9, generated through the 1,2-rearrangement of intermediate unstable tricyclic thiophenium ylide 10, but also a product of insertion into the C7H bond (11). 37 New stable four-to-seven-membered cyclic ylides were synthesised by intramolecular cyclisation of diazosulfides and their thermal rearrangements giving rise to heterocyclic compounds were carried out virtually simultaneously by two independent research groups. 38 ± 40 It was demonstrated 38,39 that six-and seven-membered cyclic ylides 12a,b underwent the 1,2-Stevens rearrangement on heating to give the corresponding substituted cyclic thioesters 13a,b in 40% ± 60% yields.…”