π-Stacking-Controlled Dearomatic Sulfur-Shifted Ene Reaction of Ketenes and Polycyclic Arylthiiranes: Access to Areno[d]-ε-thiolactones

Abstract

Electrophilic ring-expansion of polycyclic arylthiiranes and ketenes generated from alkoxy/aryloxyacetyl chlorides in the presence of triethylamine (TEA) is developed and provides a new strategy for the synthesis of areno[d]-ε-thiolactones, areno[d]thiepinones, directly without catalysts or additives. This strategy features atom-and step-economic one-pot characteristic via a tandem sequence of in situ ketene generation, π-stacking-controlled dearomatic sulfur-shifted ene, and aromatization. The current reaction is a novel strategy of electrophilic ring expansions of three-membered saturated heterocycles.

Linear Free Energy Analysis on the Ring‐Expansion of Arylthiiranes with Ketenes

“…Although the optimizations on the reaction conditions were further performed with phenoxyacetyl chloride (1 a) and ([1,1'biphenyl]-4-yl)thiirane (2 a) as the model substrates, the best conditions were still that they were stirred in the presence of triethylamine in toluene at 100 °C for 30 min as the previous optimizations. [19] To further evaluate the reactivity of different phenylthiiranes 2 and to perform a linear free energy analysis on the ring expansion, the reactions of phenoxyacetyl chloride (1 a) and different para-substituted phenylthiiranes were carried out under the optimal reaction conditions. The results were summarized in Table 1.…”

“…The reaction is a tandem process of π-stacking controlled dearomatic sulfur-shifted ene reaction followed by aromatization (Scheme 1d). [19] Different chemoselectivities were observed in these reported reactions. We are interested in the chemistry and chemoselectivity in the ring expansion of different thiiranes and ketenes.…”

“…Melting points were measured using melting point apparatus and are uncorrected. 1 H, 13 C and 19 F NMR spectra were recorded on a Bruker 400 MHz spectrometer in CDCl 3 with TMS as an internal standard, and the chemical shifts (δ) are reported in parts per million (ppm). All coupling constants (J) in 1 HNMR are absolute values given in hertz (Hz) with peaks labeled as singlet (s), broad singlet (brs), doublet (d), triplet (t), quartet (q), doublet of doublets (dd), doublet of triplets (dt), and multiplet (m).…”

“…[7][8][9] However, only limited examples on electrophilic ring expansions of thiiranes with ketenes were reported to date. [16][17][18][19] For the reactions of diphenylketene and thiiranes, phenylthiirane, 2,2-dimethyl-3-(propan-2-ylidene)thiirane, and ethenylthiirane generated 3,3,4triphenyldihydrothiophen-2(3H)-one (γ-thiolactone) in the presence of lithium chloride (Scheme 1a), [16] 2-(diphenylmethylene)-5,5-dimethyl-4-(propan-2-ylidene)-1,3-oxathiolane under heating (Scheme 1b), [17] and 2-(diphenylmethylene)-5-ethenyl-1,3oxathiolane under the palladium catalysis (Scheme 1c), [18] respectively. Only one example was reported in each of reactions.…”

Recent Advances in π-Stacking Interaction-Controlled Asymmetric Synthesis

“…After aromatization, intermediates 65 transform into the final products 66 in 22−94% yields. The current reaction features atom and step-economic characteristics via a tandem sequence of in situ ketene generation, π-stacking-controlled dearomatic sulfur-shifted ene, and aromatization and is a novel strategy for the electrophilic ring expansions of three-membered saturated heterocycles (Scheme 12) [55]. The nucleophilic ring expansion of saturated three-membered heterocycles has been well investigated [52].…”