One-Pot O₂-Oxidation and the Horner–Wadsworth–Emmons Reaction of Primary Alcohols for the Synthesis of (Z)-α,β-Unsaturated Esters

Abstract

We developed one-pot oxidation/olefination procedures of primary alcohols giving Z-α,β-unsaturated esters 3. TEMPO-(CuCl or CuBr2)-(2,2′-bipyridine) (1:1:1) catalyzed O2 oxidation of primary alcohols in the presence of Z-selective Horner–Wadsworth–Emmons reagent 1b and K3PO4 or NaH gave 3 with Z/E = 84:16 to 96:4 in high yields. A stepwise reaction was also developed. After TEMPO-CuBr2-(2,2′-bipyridine)-K3PO4 (1:1:1:1) catalyzed O2 oxidation of alcohols in MeCN, the resulting mixture was treated with a THF solution of 1b and t-BuOK at −78 °C to 0 °C, giving 3 with higher selectivity (Z/E = 91:9 to 99:1).

A Metallomicellar Catalyst for Controlled Oxidation of Alcohols and Lignin Mimics in Water using Open Air as Oxidant

“…To begin with our catalytic investigation towards the oxidation/oxidative cleavage of lignin model compounds, initially we subjected 2‐(4‐methoxyphenoxy)‐1‐phenylethan‐1‐ol ( 60 a ) under the standard conditions, as a model reaction, the appropriate carbonyls ( 60 b and 60 c ) were isolated in 86 and 83 % yields, with phenol in 12 % yield as another cleaved product (entry 1, Table 4). The observed low yield for phenol is probably due to its instability and easy oxidizable under the reaction conditions [35] . Inspired by the obtained results, we screened other substrates, 2‐phenoxy‐1‐phenylethanol derivatives ( 61 a – 63 a ), where the phenoxy group is substituted with methoxy functionalities at different positions under the standard conditions (Table 4).…”

“…The observed low yield for phenol is probably due to its instability and easy oxidizable under the reaction conditions. [35] Inspired by the obtained results, we screened other substrates, 2-phenoxy-1-phenylethanol derivatives (61 a-63 a), where the phenoxy group is substituted with methoxy functionalities at different positions under the standard conditions (Table 4). Fortunately, all the lignin model compounds were successfully oxidized/oxidatively cleaved into the corresponding carbonyls viz ketones and acids exclusively in noticeable yields (entries 2-4, Table 4).…”

“…Some effective methodologies have been developed for the oxidation of alcohols and oxidative cleavage of C−C bonds, including β ‐O‐4 linkages using metal‐based catalysts during the past decades [16–51] . Such traditional procedures involve the addition of stoichiometric amounts of oxidants, or metal components like manganese(IV) or chromium(VI) based reagents (Figures 1a and 2a).…”

“…In a constant search for cleaner (“greener”) technologies, oxygen is undoubtedly the most ubiquitous, atom‐economical, and environmentally benign oxidant, that produces water as the only by‐product [25] . In recent times, a few other protocols for oxidation/oxidative functionalization of alcohols and C−C bonds utilizing transition metal‐based catalysts [26–51] have been reported (Figures 1b and 2b). Nevertheless, many of the recently evolved methodologies that could use oxygen/air as the sole oxidant suffer from the limitations of either toxic or harsh reaction conditions and require specialized components like noble/bimetallic catalysts, external ligands, free radical additives, and/or common organic solvents.…”