Stereocontrolled [4+1] Annulation of α‐Hydroxycyclobutenones: Synthesis of Polysubstituted Cyclopentenones

Abstract

As tereocontrolled [4+ +1] annulation of ahydroxycyclobutenonesh as been disclosed. Fort he first time, a-hydroxycyclobutenones have been proven as facile diene precursors for [4+ +1] annulation. Meanwhile,t he reported transformation presents ac oncise synthetic route to polysubstituted cyclopentenones with high stereoselectivity.

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

“…A number of cycloaddition reactions of cyclobutenones have been reported, and most of them have been summarized in the review published in 2016 . New entries include cycloaddition reactions of cyclobutenone 320 with imine 321 and diazomethane 323 , and a cycloaddition reaction of benzocyclobutenone 254 with isatin 325 (Scheme ). …”

“…They are kinetically inert and thermodynamically stable, and thus, difficult to cleave. 1 When they are structurally strained, however, their cleavage becomes significantly more feasible. Release of the structural strain offers a dynamic momentum as well as a thermodynamic driving force for their transformations.…”

Synthesis of Alkoxycarbonyldifluoromethyl-Substituted Semisquarates and Their Transformations

“…Recently, Hu and co-workers reported the stereoselective transformation of 4-hydroxycyclobutenones into polysubstituted 5-(trimethylsilyl)cyclopentenones by formal [4 + 1] annulation with trimethylsilyldiazomethane (TM-SCHN 2 ). 13 Because cyclopentenones are useful building blocks for the synthesis of bioactive molecules, 14 T. Kurohara et al…”

“…The observed relative configurations of 11f were in good agreement with the mechanism originally proposed by Hu and co-workers. 13 We previously demonstrated that the CF 3 -semisquarate can be efficiently functionalized by electrophilic addition of unsaturated organosilanes. 5b Thus, the compatibility of the EtO 2 CCF 2 group with Lewis acid promoted Hosomi-Sakurai-type allylation and Mukaiyama-type aldol reaction conditions was investigated (Scheme 7).…”

“…1 H NMR chemical shifts are reported in terms of chemical shift (δ, ppm) relative to the singlet at δ 7.26 for chloroform. 13 C NMR spectra were fully decoupled and are reported in terms of chemical shift (δ, ppm) relative to the triplet at δ 77.0 for CDCl 3 . 19 F NMR spectra are reported in terms of chemical shift (δ, ppm) relative to the singlet at δ -63.7 for α,α,α-trifluorotoluene as an external standard.…”