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Irradiation of a solution of dicinnamates of o-bis(3-hydroxy-1-oxapropyl)benzene and o-bis(6-hydroxy-1,4-dioxahexyl)benzene in methanol by Pyrex-filtered UV light gave the corresponding intramolecular pseudophotodimerized crown ethers, and irradiation of the crown ethers in methanol by 220 nm UV light gave the open chain starting dicinnamates in reverse. The structures of the isolated crown ethers were confirmed to be δ-form by the 1H NMR spectra and X-ray analysis.

In the presence of niobium pentachloride (NbC15), an atrialkylstannylmethyl-P-keto ester is homologated to the corresponding y-keto ester in good yield; the reaction mechanism is discussed.

Niobium Pentachloride-Mediated Novel Homologation Reactions Using . alpha.-Trialkylstannylmethyl-β-keto Esters.-Treatment of α-trialkylstannylmethyl-β-keto esters with NbCl5 provides the corresponding homologated γ-keto esters (cf. ( II), (IV)) in good yield. A plausible reaction mechanism is proposed. -(YAMAMOTO, M.; NAKAZAWA, M.; KISHIKAWA, K.; KOHMOTO, S.; Chem.