Chiral laser photochemistry: photoresolution accompanying photoisomerization of (±)-1-acetyl(benzoyl)aminobicyclo[3.2.0]hepta-3,6-dien-2-one to optically active 7-isomers. A photochemical procedure for chirality enhancement of (–)-(1S,5S)-7-acetylaminobicyclo[3.2.0]hepta-3,6-dien-2-one

Abstract

Photoisomerization of (±)-1-acetylaminobicyclo [3.2.0]hepta-3,6-dien-2-one (±)-(2b) with u.v. left circularly polarized light up to 36% conversion led to (–)-(1S,5R)-(2b)[optical purity, o.p. 0.83%; Δε_max.(347)–4.2 dm³ mol^–1 cm^–1] and (–)-(1S,5S)-7-acetylaminobicyclo[3.2.0]hepta-3,6-dien-2-one (–)-(3b)[o.p. 1.5%; Δε_max.(345)–3.3]. The optical purities obtained allowed us to measure circular dichroism for λ > 260 nm. An analogous procedure when applied to the benzoylamino-derivatives gave Δε_max.(348)–5.0 and Δε_max.(346)–4.9 for the 1- and 7-derivatives, respectively. Further chirality enhancement to o.p. 2.9% permitted a complete (>200 nm) c.d. spectrum to be obtained for (–)-(3b).