Anionic activation of the Wittig reaction using a solid-liquid phase transfer: examination of the medium-, temperature-, base- and phase-transfer catalyst effects

Abstract

Potassium carbonate is a remarkable base in the Wittig reaction. It promotes the formation of ethylenic compounds in excellent yields, by a biphasic solid-liquid process. There is modest reactivity in the presence of hydroxides. The Z-isomer is the major product in aprotic media whereas the E-isomer is promoted in protic media. The addition of phase-transfer agents accelerates the reaction. However sodium hydroxide on alumina can be used as the basic system for the Wittig reaction.

Stereoselective Synthesis of Unsaturated and Functionalized l-NHBoc Amino Acids, Using Wittig Reaction under Mild Phase-Transfer Conditions

“…When the experiments were performed in THF, using a strong base such as LiHMDS, LDA, n -BuLi, or t -BuLi, the corresponding unsaturated amino acids 11a were obtained with low yields and partially racemized. As the phosphonium salt 4 may act as a phase-transfer agent, we have envisaged to perform the reaction in heterogeneous conditions, using an inorganic weak base (Scheme , Table ) …”

“…The use of Li 3 PO 4 or NaH as base in chlorobenzene at 90 °C did not lead to the formation of the product 11a (entries 5, 6). When K 2 CO 3 is used in 1,4-dioxane and in the presence of 0.8 equiv of water, 11a was obtained in 58% yield (entry 7). Finally, the best result was obtained when the amino acid phosphonium salt 4 is heated during 15 h in chlorobenzene with benzaldehyde 10a in the presence of dry K 3 PO 4 (entry 8) .…”

1H NMR Analysis of the Metathesis Reaction between 1-Hexene and (E)-Anethole Using Grubbs 2nd Generation Catalyst: Effect of Reaction Conditions on (E)-1-(4-Methoxyphenyl)-1-hexene Formation and Decomposition

“…The isomerization [27][28][29][30] of hex-1ene (1), 5-decene (5) and heptene (10) and the participation of these isomers, together with other metathesis by-products such as ethene (6), propene (4) and butene (8) in metathesis reactions, cannot be excluded. Certain resonances may thus be ascribed to the expected compounds and homologues thereof: the ddt corresponding to H-2 of hex-1-ene (1) may therefore also be ascribed to other terminal alkenes; the dd corresponding to H-1 of (E)-1-(4-methoxyphenyl)-1-hexene (3) may include H-1 of homologues with four or more carbons in the side chain, and the multiplet corresponding to H-5 of 5-decene (5) may include other internal alkene resonances [31,32]. The time trace of experiment 4, prepared from the data obtained in Figure 4, appear in Figure 5.…”

Visible Light-Mediated Quantum Dot Photocatalysis Enables Olefination Reactions at Room Temperature

“…One of the most popular methods to introduce double bonds in organic molecules was developed by George Wittig in 1953, which consists of a two-step reaction involving the formation of phosphonium ylides and its subsequent reaction with carbonyl moieties to yield the desired alkenes . However, the classical Wittig reaction often requires conditions such as usage of high temperature (≥100 °C) and strong bases. , The wide applicability of Wittig reaction in organic synthesis has led to the development of modified strategies that require milder reaction conditions. − As a result, Wittig reactions have been accomplished at milder bases and low temperature with many stabilized phosphonium ylides, especially for the synthesis of stilbene derivatives. − The introduction of visible light photocatalysis to carry out similar olefination reactions can potentially provide added advantages in terms of sustainability as well as help unravel newer mechanistic insights of the reaction. Here, we report the use of QDs as efficient visible-light photocatalysts at room temperature for performing olefination reactions in one pot.…”