Tetrahydrofurane und γ‐Lactone, III. γ‐Lactone mit funktionalisierten γ‐ständigen Seitenketten aus Cyclooctin nnd Furan

Tetrahydrofurans and γ‐Lactones, III. — γ‐Lactones with Functionalized γ‐Side Chains from Cyclooctyne and Furan The oxanorbornadiene 1 , easily available from cyclooctyne and furan, is converted in three simple steps (hydrogenation, ozonolysis, and oxidation by air) to the γ‐substituted γ‐lactone 4a with a carbonyl and a carboxyl group in the side chain. The corresponding methyl ester 4b gives by diastereoselective reduction the esters (±)‐ syn ‐ and anti ‐ 5 , which are fully characterized as pure crystalline compounds. Reduction of 4a with borane and subsequent oxidation with pyridinium chlorochromate leads to the aldehyde 4d via hydroxylated derivatives.