Synthesis of Functionalized Bicyclo[3.2.0]heptanes – a Study of the [2+2] Photocycloaddition Reactions of 4‐Hydroxycyclopent‐2‐enone Derivatives

Abstract

A selection of 4-hydroxycyclopent-2-enone derivatives were prepared in enantiomerically pure form, and their photochemical [2+2] cycloaddition reactions with a variety of alkenes were studied, with a view to providing diversely functionalized bicyclo[3.2.0]heptanes. Intermolecular reactions provided the target structures in reasonable yields as a mixture of exo and endo adducts, in proportions which varied

Chemistry of 4‐Hydroxy‐2‐cyclopentenone Derivatives

“…[85] Aitken et al compared the inter-and intramolecular modes of [2+2] photocycloadditions using diversely functionalised 4-hydroxy-2-cyclopentenones and a selection of alkenes (Scheme 44). [86] The intermolecular reactions of 240 to give products 241 were for the most part bereft of any significant stereoselectivity, while the intramolecular reaction of 242 furnished 243 as the unique product, in 60 % yield. In a similar vein, Greaney et al [87] carried out an intramolecular Paternò-Büchi photochemical [2+2] reaction between the ketone side chain and the carbon-carbon double bond of the 4-oxygenated 2-cyclopentenone subunit of compound 244, which delivered the tetracyclic compound 245 with excellent yield and stereoselectivity (Scheme 45).…”

Diastereodifferentiating [2+2] photocycloaddition of chiral cyclohexenone carboxylates with cyclopentene by a microreactor

“…Previously, we reported on the synthesis of some (racemic) natural products and cyclopentenoids via this photoreaction [5]. Among these valuable syntheses, in particular, asymmetric [2+2] photocyclization has attracted much attention in the synthetic field because this asymmetric photoreaction can easily produce enantiomeric pure cyclobutane scaffolds [6][7][8][9][10][11]. We have already elucidated that diastereodifferentiating [2+2] photocycloaddition of cyclohexenone carboxylates using menthol derivatives as chiral auxiliaries is one of the most effective methods for chiral induction [12][13][14][15].…”

Total Synthesis of (±)‐Hippolachnin A

“…Irradiation of 3 and hex‐3‐yne in acetone at λ >270 nm afforded bicyclo[4.2.0]heptanone 4 in a diastereomeric ratio of 4:1 10. 11 As the photoadduct was susceptible to elimination to form enone 5 during chromatography, ketone 4 was not isolated but directly converted into 5 . Treatment of the unpurified photoreaction mixture with deactivated alumina and potassium carbonate furnished enone 5 in 54 % overall yield over two steps 12…”