1,2‐Diarylethanols by Alternative Regioselective Reductive Ring‐Opening of 2,3‐Diaryloxiranes

Abstract

Keywords: Epoxides / Ring-opening reactions / Reduction / Alcohols / Enantioselectivity / Regioselectivity Non-symmetrical trans-2,3-diaryloxiranes have been regioselectively opened by catalytic hydrogenation over Pd/C, NaBH 4 /Pd and [Cp 2 TiCl]/H 2 O. Although in the catalytic hydrogenation reactions the epoxides were mainly opened at the β-carbon with respect to the substituted aryl ring in all cases, with the [Cp 2 TiCl]/H 2 O system the regioselectivity was affected by the electronic properties of the aryl residues, the epoxides being opened on the carbon bearing the most

Base‐Promoted Heterogeneous Reusable Copper Fluorapatite (CuFAP) Catalyzed Facile Synthesis of 1,2‐Diarylethanols via C(sp3)‐H Functionalization of Nitrotoluene

“…Lupattelli et al . have reported the regioselective reductive ring‐opening of 2,3‐diaryloxiranes by catalytic hydrogenation over Pd/C, NaBH 4 /Pd and [Cp 2 TiCl]/H 2 O, whereas Doyle et al . have reported Ni‐catalyzed cross‐coupling of styrenyl epoxide with boronic acids in the presence of ligand and additive .…”

“…have reported Ni‐catalyzed reductive benzylation of aldehydes with benzyl halides and pseudohalides in the presence of ligand and additive . Nonetheless, all these approaches reported lacks practical approach and hence suffer one or other drawbacks such as use of prefunctionalized substrates,, costly precious metal catalysts,, and highly expensive ligands,, additives,, hazardous, toxic reagents,,,, and harsh reaction conditions, as well as incompatibility of catalysts with prefunctionalized substrates causes the occurrence of an unexpected side reaction, consequently low yield of the desired product ,,…”

“…[3] Even though 1,2-diarylethanol has its potent important in life sciences/ pharmaceutical, surprisingly, so far only a few strategies for its synthesis have been reported by researchers. Lupattelli et al have reported the regioselective reductive ring-opening of 2,3diaryloxiranes by catalytic hydrogenation over Pd/C, NaBH 4 /Pd and [Cp 2 TiCl]/H 2 O, [4] whereas Doyle et al have reported Nicatalyzed cross-coupling of styrenyl epoxide with boronic acids in the presence of ligand and additive. [5] Moreover, Du et al have reported reaction between a variety of toluene derivatives and aldehydes under conventional heating and ultrasound irradiation using inorganic base.…”

“…[7] Nonetheless, all these approaches reported lacks practical approach and hence suffer one or other drawbacks such as use of prefunctionalized substrates, [4,5] costly precious metal catalysts [4,5,7] and highly expensive ligands, [5,7] additives, [5,7] hazardous, toxic reagents, [4,5,6,7] and harsh reaction conditions [5,6] as well as incompatibility of catalysts with prefunctionalized substrates causes the occurrence of an unexpected side reaction, consequently low yield of the desired product. [4,5,6] Owing to the potential utility of 1,2-diarylethanol in the pharmaceutical, and organic synthesis as structural backbone, cost-effective, sustainable, environmentally friendly synthesis of its structural units under mild reaction conditions by avoiding the use of costly ligands, precious metal catalysts, additives, prefunctionalized substrates, and toxic, hazardous reagents is still challenging and an active research area. The CÀH functionalization has been continuously increasing interest among chemist/biologist, which provides a straightforward approach for the synthesis of complex scaffolds [8] using cheap and readily available starting materials under milder reaction conditions by avoiding the use of prefunctionalized substrates and thus provides an environmentally benign and economically attractive approach.…”

Electronic and chelation effects on the unusual C2‐methylation of N‐(para‐substituted)phenylaziridines with lithium organocuprates

“…It is well known that the ring‐opening reactions of most three‐membered heterocycles (e.g., oxiranes, aziridines, and thiiranes) usually lead to both the more hindered C2 opening ( minor ) and the less hindered C3 opening ( major ). The regioselective C2‐opening reactions have been achieved depending on the following conditions: C2 aromatic activations,9–11 heteroatom activations (e.g., N‐activating groups or aziridinium salts),12–15 catalysts (e.g., Lewis acids, metal–ligand complexes, metal oxides, and organic/inorganic catalysts),16–32 unique nucleophiles,33–38 and C2‐driecting effects of nucleophiles 39–42. Despite previous theoretical studies on the ring‐opening mechanism,43–56 little have been explored in regard to the favored opening at the more‐hindered C2 atom,57–61 especially at the benzylic C2 atom 62, 63.…”