Rhodium(i)-catalyzed asymmetric [4 + 2] cycloaddition reactions of 2-alkylenecyclobutanols with cyclic enones through C–C bond cleavage: efficient access totrans-bicyclic compounds

Abstract

We report a rhodium-catalyzed asymmetric formal intermolecular [4 + 2] cycloaddition reaction of 2-alkylenecyclobutanols with α,β-unsaturated cyclic ketones leading to synthetically useful trans-bicyclic molecules.

Cleavage of Carbon–Carbon σ-Bonds of Four-Membered Rings

“…Selective cleavage of the C­(sp 2 )–C­(sp 3 ) bond is observed also with 2-alkylidenecyclobutanol 117 (Scheme ). , …”

“…The ring-opening reaction was further combined with insertion reactions of enones, nitroolefins, and alkynes (Scheme ).…”

“…53,54 Selective cleavage of the C(sp 2 )−C(sp 3 ) bond is observed also with 2-alkylidenecyclobutanol 117 (Scheme 28). 55,56 The ring-opening reaction was further combined with insertion reactions of enones, 55 nitroolefins, 57 and alkynes 57 (Scheme 29).…”

RuPHOX-Ru-Catalyzed Selective Asymmetric Hydrogenation of Exocyclic α,β-Unsaturated Pentanones

“…Initially, the RuPHOX-Ru-catalyzed asymmetric hydrogenation of (E)-2-benzylidenecyclopentan-1-one (1a) was carried out under 20 bar of hydrogen pressure with 1 equiv of DBU as a base in different solvents at room temperature for 1 h. 11 As shown in Table 1, MeOH was first used as a solvent with the desired product (R,E)-2-benzylidenecyclopentan-1-ol (2a) being obtained in quantitative conversion and 99.5% ee (entry 1). The use of EtOH provided the same conversion but a slightly lower enantioselectivity in comparison to that of MeOH (entry 2).…”

“…The CC double bond of 2a could be further reduced using Pd/C as a catalyst in THF, affording the corresponding 3 in 99% yield, 2:1 dr, and 99% ee. The CC double bond could also be oxidized by m -CPBA to give the corresponding epoxidation product 4 in 83% yield without any loss in enantioselectivity …”