Academic literature on the topic 'Nucleophilic addition'

The products of the reactions of 2-(4-methoxyphenyl)ethyl tosylate (MeO-1-OTs) and 2-(4-methyphenyl)ethyl tosylate (Me-1-OTs) with nucleophilic anions were determined for reactions in 50:50 (v/v) trifluoroethanol (TFE) / water at 25 °C. In many cases, the nucleophile selectivity kNu/ks ((mol/L)−1) for reactions of nucleophile and solvent, calculated from the ratio of product yields, depends upon [Nu−]. This demonstrates the existence of competing reaction pathways, which show different selectivities for reactions with nucleophiles. A 13C NMR analysis of the products of the reactions of substrate enriched with 13C at the α-carbon, X-1-[α-13C]OTs (X = −OCH3 or −Me), with nucleophilic anions in 50:50 (v/v) TFE/water at 25 °C shows the formation of X-1-[β-13C]OH, X-1-[β-13C]OCH2CF3, and X-1-[β-13C]Nu (Nu = Br, Cl, CH3CO2, or Cl2CHCO2) from the trapping of symmetrical phenonium ion reaction intermediates X-2+. The observation of excess label in the α-position, [α-13C]/[β-13C] > 1.0, for both the water and nucleophile adducts, shows that these nucleophiles also react by direct substitution at X-1-[α-13C]OTs. The ratios of product yields, [α-13C]/[β-13C], and observed nucleophile selectivity (kNu/ks)obs were used to dissect the contribution of nucleophile addition at Me-1-OTs and trapping of X-2+ to the product yields. The product yields from partitioning of the intermediate gave the nucleophile selectivity kNu/ks for X-2+. Swain–Scott plots of log(kNu/ks) are correlated by slopes of s = 0.78 and s = 0.73 for reactions of MeO-2+ and Me-2+, respectively. This shows that the sensitivity of bimolecular substitution at X-2+ to changes in nucleophile reactivity is smaller than for nucleophilic substitution at the methyl iodide.

A variety of α,β-unsaturated acetylenic ketones, prepared in good yields from 3,3,4,4-tetraethoxybut-1-yne (TEB), have been reacted with selected mono- and bis-nucleophilic reagents. The mononucleophiles react in a Michael fashion and give in most cases the corresponding α,β-unsaturated alkenones in good yield. Many of the alkenes are formed as single stereoisomers, but the configuration depends on the nature of the nucleophile. If hydrogen bonds can be formed, the Z geometry is preferred, otherwise the E geometry is completely predominant. Experiments have also uncovered that α,β-unsaturated acetylenic ketones with a gem-diethoxy moiety in the α' position decompose when reacted with sodium hydroxide in aqueous tetrahydrofuran (THF); the carbonyl group is attacked and a carboxylic acid and a terminal alkyne are formed. If the nucleophiles contain two nucleophilic centers or if the α,β-unsaturated acetylenic ketones contain an additional reactive group, such as a hydroxyl group or an acyloxy moiety, useful secondary reactions may occur. By taking advantage of such secondary transformations, two completely regioselective syntheses of furans have so far been developed.