Sunlight is the ultimate driver of biosynthesis but photochemical steps late in biosynthetic pathways are very rare. They appear to play a role in the formation of certain furanocembranoids isolated from Caribbean corals. One of these compounds, intricarene, has been suspected to arise from an intramolecular 1,3-dipolar cycloaddition involving an oxidopyrylium. Here we show, by a combination of experiments and theory, that the oxidopyrylium forms under photochemical conditions and that its cycloaddition occurs via a triplet state. The formation of a complex by-product can be rationalized by another photochemical step that involves a conical intersection. Our work raises the question whether intricarene is biosynthesized in the natural habitat of the corals or is an artefact formed during workup. It also demonstrates that the determination of exact irradiation spectra, in combination with quantum chemical calculations, enables the rationalization of complex reaction pathways that involve multiple excited states.

SummaryWe report the elusive X-ray structure of the Dess–Martin periodinane (DMP), a hypervalent iodine reagent popular amongst synthetic chemists. In the solid state, the highly crystalline compound forms an intricate coordination polymer held together by intermolecular halogen and hydrogen bonds.

Crocagin A (1) combines an attractive molecular structure with an unusual biosynthesis and bioactivity. An efficient synthesis of crocagin A is presented that hinges on an early formation of the heterotricyclic core, an electrophilic amination, and the stereoselective hydrogenation of a tetrasubstituted double bond. This synthesis confirms the absolute configuration of crocagin A and provides access to the natural product and derivatives thereof for further biological testing.

Crocagin A( 1)c ombines an attractive molecular structure with an unusual biosynthesis and bioactivity.A n efficient synthesis of crocagin Aispresented that hinges on an early formation of the heterotricyclic core,a ne lectrophilic amination, and the stereoselective hydrogenation of atetrasubstituted double bond. This synthesis confirms the absolute configuration of crocagin Aand provides access to the natural product and derivatives thereof for further biological testing. Scheme 1. Structure and biosynthetic origin of crocagin.Scheme 2. Retrosynthetic analysis of crocagin A.