Photochemical Cycloaddition as a Gateway to Bicyclic Lactones: Toward Tricyclic Iridoid-Inspired Scaffolds

A photochemical [2 + 2] cycloaddition between cyclopentene-1-one and 1,1-dimethoxyethylene was effectively utilized to synthesize a key bicyclic intermediate in the preparation of tricyclic iridoid-inspired scaffolds. The regioselective outcome of the cycloadduct was confirmed through ¹H NMR and subsequent chemical reactivity studies, indicating that the methoxy groups do not occupy positions β to the carbonyl. Following this, hydrolysis of the cycloadduct yielded a diketone in an excellent yield of 85%, which was subsequently subjected to Baeyer–Villiger oxidation, resulting in a fused γ-lactone with a yield of 64%. Structural elucidation of the intermediates and the final product was conducted using NMR, IR, and mass spectrometry techniques. This photochemical synthetic pathway offers a concise approach to bioinspired tricyclic architectures that may hold significance in natural product chemistry and the design of neuroactive compounds.