“…However, rather than carbonylating, as in Pauson–Khand‐type reactions, the oxaruthenacycles undergo reduction by dehydrogenating alcohol reactants, releasing product, and regenerating the carbonyl partner required for oxidative coupling. This pattern of reactivity served as the basis for the design of novel [4+2] cycloadditions of 1,2‐diols with dienes, and α‐ketols with 3,4‐benzannulated 1,5‐diynes . Herein, we report that zero‐valent ruthenium catalysts promote the [4+2] cycloaddition of α‐ketols with ortho ‐acetylenic benzaldehydes, and demonstrate how this transformation enables concise construction of ring systems found in type II polyketides of the angucycline class .…”