Metal‐Free Tandem Rearrangement/Lactonization: Access to 3,3‐Disubstituted Benzofuran‐2‐(3H)‐ones

Abstract

An ovel metal-free synthesis of 3,3-disubstituted benzofuran-2-(3H)-ones through reacting a-aryl-a-diazoacetates with triarylboranes is presented. Initially,t riarylboranes were successfully investigated in a-arylations of a-diazoacetates,h owever in the presence of ah eteroatom in the ortho position, the boron enolate intermediate undergoes an intramolecular rearrangement to form aq uaternary center.T he intermediate cyclizes to affordv aluable 3,3-disubstituted benzofuranones in good yields.

1,3-Carboboration of iodonium ylides

“…15 Recently, our group reported that transfer of other halogenated aryl groups to diazo species is possible (Scheme 1c). 16 Given the analogous nature between diazo species and iodonium ylides as carbene precursors, 17 we envisaged that a similar aryl transfer should be viable. To this end, we divulge the reaction of iodonium ylides with a library of boranes (BAr F 3 ; Ar F = 3,4,5-F 3 C 6 H 2 (1a), 2,4,6-F 3 C 6 H 2 (1b), 2,6-F 2 C 6 H 3 (1c), C 6 H 5 (1d) and C 6 F 5 (1e)) displaying varying levels of Lewis acidity (Scheme 1d).…”

Single Electron Transfer to Diazomethane–Borane Adducts Prompts C−H Bond Activations

“…In 2012, we reported the insertion of diazomethanes into B−C bonds of electrophilic boranes with the liberation of N 2 (Scheme ) . Such insertions were recently exploited in organic synthesis by Melen et al . In recent work, we showed that the sterically‐encumbered diazomethane, Ph 2 CN 2 , does not insert but rather forms a highly reactive, yet isolable borane‐adduct, (Ph 2 CN 2 )B(C 6 F 5 ) 3 .…”

Single Electron Transfer to Diazomethane–Borane Adducts Prompts C−H Bond Activations

“…[22] In 2012, we reported the insertion of diazomethanes into BÀCb onds of electrophilic boranes with the liberation of N 2 (Scheme 1). [23] Such insertions were recently exploited in organic synthesis by Melen et al [24] In recent work, [25] we showed that the sterically-encumbered diazomethane,P h 2 CN 2 ,d oes not insert but rather forms ah ighly reactive,y et isolable borane-adduct, (Ph 2 CN 2 )B(C 6 F 5 ) 3 . Moreover,w ea lso showed weak Lewis acid-base adducts were stabilized by stoichiometric reduction.…”