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%; Δεmax.(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%; Δεmax.(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 Δεmax.(348)–5.0 and Δεmax.(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).

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