Stereodivergent Intramolecular C(sp³)–H Functionalization of Azavinyl Carbenes: Synthesis of Saturated Heterocycles and Fused <i>N</i>‑Heterotricycles

A general approach for the formation of five-membered saturated heterocycles by intramolecular C­(sp3)–H functionalization is reported. Using N-sulfonyltriazoles as Rh­(II) azavinyl carbene equivalents, a wide variety of stereodefined cis-2,3-disubstituted tetrahydrofurans were obtained with good to excellent diastereoselectivity from readily available acyclic precursors. The reaction is shown to be amenable to gram scale, and judicious choice of reaction conditions allowed for stereodivergence, providing selective access to the trans diastereomer in good yield. The resulting products were shown to be valuable intermediates for the direct preparation of fused N-heterotricycles in one step by intramolecular C–H amination or Pictet–Spengler cyclization.本研究报道了一种通过分子内C(sp³)-H官能团化反应构建五元饱和杂环的通用策略。以N-磺酰基三唑作为铑(II)氮烯基卡宾等价物，以易得的无环前体为起始原料，可得到一系列立体构型明确的顺式-2,3-二取代四氢呋喃，产物表现出良好至优异的非对映选择性。该反应可拓展至克级规模，且通过合理选择反应条件可实现立体发散，以较高收率选择性得到反式非对映异构体。研究证实，所得产物可作为关键中间体，通过分子内C-H胺化或皮克特-斯彭格勒环化反应，一步直接制备稠合氮杂三环化合物。