An Umpolung Oxa-[2,3] Sigmatropic Rearrangement Employing Arynes for the Synthesis of Functionalized Enol Ethers

Abstract

An oxa-[2,3] sigmatropic rearrangement involving arynes is reported featuring the umpolung of ketones, where the CO bond polarity is reversed. The in situ-generated sulfur ylides from β-keto thioethers and arynes undergo efficient rearrangement allowing the facile and robust synthesis of functionalized enol ethers in high yields and excellent functional group compatibility. Preliminary mechanistic studies rule out the possibility of Pummerer-type rearrangement operating in this case.

Synthesis of C2‐Functionalized Pyrimidine Derivatives by Using Arynes and Dithiopyrimidines

“…When asymmetric 4-methyl-2-(trimethylsilyl)phenyl trifluoromethanesulfonate 2 b is reacted with 1 a, regional isomers 3 v/3 v' (10 : 9) compounds are obtained in 75 % yield. The regioisomers ratio was detected by 1 H NMR analysis of the mixture product.. [12] When the symmetric 4,5dimethyl-2-(trimethylsilyl)phenyltrifluoro methanes-ulfonic acid 2 c and 4,5-difluoro-2-(trimethylsilyl) phenyltrifluoromethanesulfonic acid 2 d and 4,5-dimethoxy-2-(trimethylsilyl) phenyltrifluoromethane-sulfonic acid 2 e were used, the desired products 3 w, 3 x and 3 y are obtained in 80 %, 42 % and 78 %, respectively. It worth mentioning here that, when large steric hindrance substrate 3-(trimethylsilyl)-2-naphthyl trifluoro-methanesulfonate 2 f was used as an arryne precursor, the target compound 3 y was also obtained in 71 % yield.…”

Transition metal-free [2,3]-sigmatropic rearrangement in the reaction of sulfur ylides with allenoates

“…However, recently the metal free version of the thia–Sommelet–Hauser reaction has been independently established by Biju and Tan groups, 7 involving only aromatic rings and requiring allyl or propargyl thioethers. Mechanistically, these reactions proceed through a benzyne intermediate and in situ formation of a sulfur ylide.…”

Synthesis of Trisubstituted Oxazoles via Aryne Induced [2,3] Sigmatropic Rearrangement–Annulation Cascade

“…In the context of our general interest in the transition-metal-free reactions engaging arynes, we have recently demonstrated the aryne oxa-[2,3] sigmatropic rearrangement highlighting the umpolung of ketones . These reactions proceed via the in situ generation of sulfur ylides A from β-keto thioethers, and arynes generated from the Kobayashi precursor, resulting in the synthesis of enol ether derivatives (Scheme A) .…”

“…Motivated by our previous work on the oxa-[2,3] sigmatropic rearrangement, the present study was initiated by the treatment of 2-substituted thio-acetonitrile 1a as a model substrate with the aryne generated from the 2-(trimethylsilyl)­aryl triflate precursor 2a using KF as a fluoride source in the presence of 18-crown-6 as an additive in CH 3 CN at 25 °C for 12 h. A facile aryne rearrangement occurred under these conditions, and the desired 2,4,5-trisubstituted oxazole derivative 3a was isolated in 72% yield (Table , entry 1). Notably, the oxa-[2,3] sigmatropic rearrangement product (derived from proton transfer from the C–H α-to the nitrile moiety) was not observed under these conditions . Moreover, the formed oxazole product 3a did not undergo the Diels–Alder reaction with aryne .…”