Two ways out of an oxetane Oxetanes are highly reactive four-membered rings that contain three carbon atoms and an oxygen atom. Recently, they were implicated as transient intermediates in Lewis acid–catalyzed intramolecular metathesis reactions of ketones with olefins. Ludwig et al. now report that by replacing the Lewis acid with a strong Brønsted acid, they can change the course of the oxetane ring-opening. In a so-called interrupted metathesis, the oxygen atom migrates and then departs through dehydration, while the remaining carbon framework cyclizes to form tetrahydrofluorene compounds. Science, this issue p. 1363 An acid-catalyzed intramolecular rearrangement forms tricyclic compounds from unsaturated ketones through a transient oxetane. Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.

中文翻译：

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通过氧原子转移中断羰基-烯烃复分解

氧杂环丁烷的两种生成方式 氧杂环丁烷是含有三个碳原子和一个氧原子的高反应性四元环。最近，它们被认为是路易斯酸催化的酮与烯烃的分子内复分解反应中的瞬时中间体。路德维希等人。现在报告说，通过用强布朗斯台德酸代替路易斯酸，他们可以改变氧杂环丁烷开环的过程。在所谓的间断复分解中，氧原子迁移然后通过脱水离开，而剩余的碳骨架环化形成四氢芴化合物。科学，这个问题 p。1363 酸催化的分子内重排从不饱和酮通过瞬态氧杂环丁烷形成三环化合物。一些最简单和最强大的碳-碳键形成策略利用了容易获得的无处不在的基序：羰基和烯烃。在这里，我们报告了羰基化合物和烯烃之间的一种根本不同的反应模式，该模式不同于已建立的酸催化羰基 - 烯、Prins 和羰基 - 烯烃复分解反应路径。一系列ε、zeta-不饱和酮经过布朗斯台德酸催化的分子内环化，通过形成两个新的碳-碳键来提供四氢芴产物。理论计算和伴随的机理研究表明，这种碳环化反应是通过氧原子转移形成的瞬态氧杂环丁烷的中介进行的。该产品类别中的复杂多环骨架作为有机材料中的常见子结构出现，