The Photochemistry of 5,6-Dimethylidene-2-norborananone. Synthesis and Diels-Alder Reactivity of 2,3-Dimethylidenebicyclo-[2.1.1]hexane

✍ Scribed by Luis Schwager; Pierre Vogel

• Publisher: John Wiley and Sons
• Year: 1980
• Tongue: German
• Weight: 347 KB
• Volume: 63
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19800630508

✦ Synopsis

Abstract

2,3‐Dimethylidenebicyclo [2.1.1]hexane (4) was isolated from direct irradiation (253.7 nm) of 5,6‐dimethylidene‐2‐norbornanone (3). Quenching experiments at 253.7 nm, as well as direct and sensitized irradiations at >300 nm suggested that a high vibrationally excited S~1~‐ or a S~2~‐state is required for the photodecarbonylation of 3 in contrast with other β, γ‐unsaturated ketones for which α‐cleavage occurs with lower excitation‐energy. The new diene 4 reacted toward tetracyano‐ethylene (k (1mol^−1^ s^−1^))=(3.1±0.34) · 10^−3^) in toluene and (6.2±0.11) · 10^−3^ in benzene only 60 times more slowly than 2,3‐dimethylidenenorbornane (5) and ca. 850 times as fast as 2,3‐dimethylidene‐__syn__1,4,5,6‐tetramethylbicyclo[2.1.1]‐hexane (9).