Construction of Spiro-γ-butyrolactone Core via Cascade Photochemical Reaction of 3-Hydroxypyran-4-one Derivatives.

We elaborate a novel one-step photochemical method for the synthesis of spiro-γ-butyrolactone derivatives from 3-hydroxypyran-4-ones. The suggested approach is based on a cascade process including initial photoinduced contraction of 4-pyranone ring followed by intramolecular cyclization leading to the final spiro system. A distinctive feature of the proposed method is intramolecular trapping of unstable α-hydroxydiketone intermediate formed in situ as a result of a photochemical reaction. The structures of two synthesized 1-oxaspiro[4.4]non-8-ene-2,6,7-triones were determined by X-ray diffraction.