Formation of Five‐Membered Cyclic Orthoesters from Tribromides with Participation of a Neighboring Carbonyl Group

Abstract

The Mg-mediated conjugate addition of bromoform to enones followed by alcoholysis of the resulting keto tribromides proceeds through an unusual course, affording cyclic orthoester (dihydrofuran) intermediates under neutral workup conditions. However, acid workup of the reaction mixture or treatment of the isolated dihydrofurans with acid provides

Visible‐Light‐Induced Direct Photocatalytic Carboxylation of Indoles with CBr4/MeOH

“…CX 3 radicals (CCl 4 =−0.78 V vs. SCE and CBr 4 =−0.30 V vs. SCE)13 by oxidative quenching of photoexcited photosensitizers 14. The intercepting of these radical species by aromatic nucleus, followed by alcoholysis,15 would deliver a rapid entry to mild CH‐type carboxylating events (Scheme B).…”

“…[12] In this context we recognized in the tetrahalogenated methanes CX 4 (X = Cl, Br) potential carboxylating agents fora renes, due to their intrinsic attitudeo fg eneratinge lectrophilic CCX 3 radicals( CCl 4 = À0.78 Vv s. SCE and CBr 4 = À0.30 Vv s. SCE) [13] by oxidative quenching of photoexcited photosensitizers. [14] The intercepting of these radical speciesb ya romatic nucleus, followed by alcoholysis, [15] would deliver ar apid entry to mild CÀH-typecarboxylating events (Scheme 1B).…”

Synthesis of α-tribromomethylamines via Mg-mediated addition of bromoform to imines

“…13,14 In the case of α-substituted enones, especially cyclic ones, the Michael adducts spontaneously cyclized to afford dibromocyclopropanation products. 14,15 Herein we report the addition of bromoform to an electron deficient carbon-heteroatom bond as in N-tosylimine and N-Boc-imine for the first time.…”

“…14,15 Herein we report the addition of bromoform to an electron deficient carbon-heteroatom bond as in N-tosylimine and N-Boc-imine for the first time. 16 Results and discussion Treatment of N-tosylimines 5 with Mg-CHBr 3 under our previous optimized conditions, [12][13][14] viz. 8 equiv.…”

“…As part of our interest in the application of Mg-CHBr 3 as a reagent system for the facile introduction of the CBr 3 group, we have reported conjugate addition of bromoform to nitroalkenes 12 and enones. 13,14 In the case of α-substituted enones, especially cyclic ones, the Michael adducts spontaneously cyclized to afford dibromocyclopropanation products. 14,15 Herein we report the addition of bromoform to an electron deficient carbon-heteroatom bond as in N-tosylimine and N-Boc-imine for the first time.…”