Metal-Free Brønsted Acid-Catalyzed Rearrangement of δ‑Hydroxyalkynones to 2,3-Dihydro‑4H‑pyran-4-ones: Total Synthesis of Obolactone and a Catechol Pyran Isolated from Plectranthus sylvestris

A metal-free, Brønsted acid, pTsOH-catalyzed intramolecular rearrangement of δ-hydroxyalkynones to substituted 2,3-dihydro-4H-pyran-4-ones was developed. The rearrangement occurs with high regioselectivity under mild and open-air conditions. The scope of work was illustrated by synthesizing an array of aliphatic and aromatic substituted 2,3-dihydro-4H-pyran-4-ones in up to 96% yield, 100% atom economy, and complete regioselectivity. Some of the dihydropyranones are utilized for vinylic halogenations and to complete the total synthesis of bioactive natural products, obolactone and a catechol pyran isolated from Plectranthus sylvestris (Labiatae).

本研究开发了一种无金属、布朗斯特酸（Brønsted acid）催化体系，以对甲苯磺酸（pTsOH）为催化剂，实现δ-羟基炔酮（δ-hydroxyalkynones）的分子内重排反应，用于合成取代的2,3-二氢-4H-吡喃-4-酮（2,3-dihydro-4H-pyran-4-ones）。该重排反应在温和敞口空气条件下可实现高区域选择性转化。通过合成一系列脂肪族及芳香族取代的2,3-二氢-4H-吡喃-4-酮类化合物，验证了该反应的底物适用范围，产物最高收率可达96%，原子经济性达100%，且区域选择性完全。部分所得二氢吡喃酮类化合物可应用于乙烯基卤代反应，并用于完成生物活性天然产物奥博内酯（obolactone）以及从唇形科（Labiatae）彩叶苏属（Plectranthus sylvestris）中分离得到的儿茶酚吡喃类化合物的全合成。