A new Julia-type methylenation reagent, 1-methyl-2-(methylsulfonyl)benzimidazole (1e), reacts with a variety of aldehydes and ketones in the presence of either NaHMDS (−55 °C to rt) or t-BuOK (rt, 1 h) in DMF to give the corresponding terminal alkenes in high yields. The byproducts are easily removed, and the reaction conditions are mild and practical.

New Peterson reagents were prepared by introducing alkyloxy groups on the silicon atom in order to fix the conformation of the sulfone anion. The reagents 1d and 1e reacted with a variety of aldehydes after the treatment with Li-base to give Z-α,β-unsaturated sulfones with up to >99:1 selectivity in good to excellent yields. For the reaction with aliphatic aldehydes, CPME (cyclopentyl methyl ether) is the choice of solvent, while DME (1,2-dimethoxyethane) gave higher selectivity for the reaction with aromatic aldehydes.

A new HWE reagent, (o-tBuC6H4O)2P(O)CH2CN (2e), reacts with various types of aldehydes to give Z-α,β-unsaturated nitriles with 86% to >99% Z-selectivity. Especially, the reaction of 2e with bulkier aldehydes, both aromatic and aliphatic, gave the Z-olefins with extremely high selectivity. The combination of t-BuOK and 18-crown-6 (1 equiv) is the base of choice for aromatic aldehydes and t-BuOK is generally the base of choice for aliphatic aldehydes.

The solvent-free Horner–Wadsworth–Emmons reaction of triethyl phosphonoacetate with a variety of aldehydes was catalyzed by DBU in the presence of K2CO3 to give E-α,β-unsaturated esters highly selectively (99:1 for most of the reactions). The reaction with ketones gave trisubstituted olefins with good to high E-selectivity by DBU-Cs2CO3.

The Z-selective intramolecular Horner–Wadsworth–Emmons reaction of the substrates 7–12 (RO)2P(O)CHR′CO2Et (R′ = (CH2)nCHO) (R = Ph or o-tBuC6H4) gives the 13–18-membered cyclic alkenes selectively (up to Z:E = 97:3) in good yields using NaH in THF under high dilution conditions.The Z-selective intramolecular Horner–Wadsworth–Emmons reaction of the substrates (Ar = Ph or o-tBuC6H4) gives the 13–18-membered cyclic alkenes selectively (up to Z:E = 97:3) in good yields using NaH in THF under high dilution conditions.

DFT computational study on the alkylation of the lithium enolate derived from acetaldehyde with MeCl was performed. The reaction of the free enolate CH2=CHO− with MeCl has an early transition state with low barrier, and the reaction of its lithium enolate gave a cyclic transition structure with high activation energy; neither of them is a good model for reaction in solution. In the presence of 1–6 THF molecule(s), a typical SN2 transition structures were obtained with reasonable activation energies after the PCM correction. Especially, the reaction in the presence of three THF molecules completed the tetra-coordination of the lithium cation, and structurally and energetically, this is an optimal model for the reaction in the solution. The transition structures were also located at the ONIOM level (high = B3LYP/6–31(+)G*: low = RHF/3–21 G*). The results are favorably compared with the full DFT results.

When the substrates (ArO)2P(O)CH2CO2---CHO (Ar = Ph, o-t-BuPh) were added to a THF solution containing 3 equiv of NaH at 0 °C or NaI−DBU at rt over 1−10 h, the intramolecular Horner−Wadsworth−Emmons reaction proceeded efficiently to give the 12−18-membered-ring lactones in 69−93% yields with 89−100% Z selectivity. On the other hand, (EtO)2P(O)CH2CO2---CHO gave the 13−18-membered-ring lactones in 52−82% yields with 89−99% E selectivity using LiCl−DBU in MeCN or THF.

The solvent-free Horner–Wadsworth–Emmons reaction with a variety of aldehydes using 1.5 equiv of DBU gave E-α,β-unsaturated esters and ketones in high yields. The E-selectivity was high and the used DBU was recovered.The solvent-free Horner–Wadsworth–Emmons reaction with a variety of aldehydes using 1.5 equiv of DBU gave E-α,β-unsaturated esters and ketones in high yields. The E-selectivity was high and the used DBU was recovered.

The reaction mechanism of the AuCl-catalyzed reaction of the α-thioallenes to give 2,5-dihydrothiophenes has been computationally studied using DFT (B3LYP/6-31G*, SDD for Au). Calculations indicate the complexation of α-thioallene with AuCl occurs preferentially at the distal double bond, followed by the C−S bond formation, the proton transfer from the sulfur to the carbon “b”, and the [1,2]-hydride shift to give the 2,5-dihydrothiophene gold complex. The proton transfer is the rate-limiting step with very high activation energy in the gas phase. In the presence of one water molecule, the activation free energy of the proton transfer was lowered by as much as 19.9 kcal/mol. Furthermore, one dichloromethane molecule stabilized all of the transition structures by its hydrogen bonds.