Novel Preparation of α,β-Unsaturated Aldehydes. Benzeneselenolate Promotes Elimination of HBr from α-Bromoacetals

Abstract

Acetalization, alpha-bromination, nucleophilic phenylselenenylation, oxidative elimination/hydrolysis was investigated as a novel protocol for the alpha,beta-dehydrogenation of aldehydes. Treatment of acetals with bromine in methylene chloride afforded the corresponding alpha-bromoacetals in 80-90% yields. Nucleophilic phenylselenenylation was then conveniently effected by treatment with benzeneselenolate generated in situ in dimethyl sulfoxide from diphenyl diselenide, hydrazine and potassium carbonate. Unbranched alpha-bromoacetals cleanly afforded substitution products whereas beta- and gamma-branched ones gave substantial amounts of alpha,beta-unsaturated acetals via formal loss of hydrogen bromide. Oxidative elimination/hydrolysis of these mixtures afforded alpha,beta-unsaturated aldehydes in 50-80% overall yields. In the case of tertiary alpha-bromoacetals, treatment with benzeneselenolate afforded only dehydrobromination products as mixtures of isomers. The presence of at least a catalytic amount of the organoselenium reagent was found to be crucial for olefin formation. A SET-mechanism, involving benzeneselenolate-induced electron transfer to the halide, loss of bromide ion, and hydrogen atom or proton/electron was proposed for the benzenselenolate-promoted elimination reaction. Experiments designed to trap carbon-centered radicals in intramolecular cyclization or ring-opening reactions failed to provide any evidence for free-radical intermediates.

Skin Sensitization of Epoxyaldehydes: Importance of Conjugation

“…The crude product was purified by column chromatography (pentane/ethyl acetate 99:1) to give 4 as a colorless oil (1.5 g, 75%). 1 H and 13 C NMR data were in agreement with those in the literature. , ESI-MS (70 eV), m / z (%) 154 (1) (M + ), 139 (9), 111 (12), 97 (35), 84 (100), 69 (27).…”

“…1 H and 13 C NMR data were in agreement with those in the literature. 36,37 ESI-MS (70 eV), m/z (%) 154 (1) (M + ), 139 (9), 111 (12), 97 (35), 84 (100), 69 (27).…”

Copolymerization of Phenylselenide-Substituted Maleimide with Styrene and Its Oxidative Elimination Behavior

“…The signals for the C=O groups in the maleimide repeat unit shifted from 173.2 to 168.6 ppm due to the formation of electron rich carbon-carbon double bond adjacent to C=O after oxidation. However, the reaction efficiency of such a reaction in the current case was lower than those found in the literature [33,34]. However, the current results clearly demonstrated that the phenylselenide substitution could be partial oxidative cleavage from maleimide by 30% H 2 O 2 , which resulted in the introducing of carbon-carbon double bonds in the backbone of copolymer.…”

“…The oxidative elimination of selenide moieties is one of the well-known reactions for selenium-containing compounds [32,33]. Herein, the obtained copolymer ([St] 0 /[MSM] 0 /[CPDN] 0 /[AIBN] 0 = 200/200/2/1, precipitated in methanol, M n = 4600 g/mol, Ð = 1.47) was treated with hydrogen peroxide (H 2 O 2 , 30%).…”

Synthesis of Mono- and Dihydroxylated Furanoses, Pyranoses, and an Oxepanose for the Preparation of Natural Product Analogue Libraries

“…The protected variant of sugar 5 was synthesized from 2-benzyloxy-5,6-dihydro-2 H -pyran ( 18 ), which originated from 3,4-dihydro-2 H -pyran ( 17 ), by treatment with phenylselenium chloride and benzyl alcohol, followed by oxidation and elimination (Scheme ). , The resulting olefin was oxidized with osmium tetroxide to furnish diol 19 . In the case of bleomycin and novobiocin, the pyranose moiety contains a carbamate in lieu of the free alcohols.…”