An Efficient Catalytic Asymmetric Epoxidation Method

Abstract

This article describes a highly effective catalytic asymmetric epoxidation method for olefins using potassium peroxomonosulfate (Oxone, Dupont) as oxidant and a fructose-derived ketone (1) as catalyst. High enantioselectivies have been obtained for trans-disubstituted and trisubstituted olefins which can bear functional groups such as tributylsilyl ether, acetal, chloride, and ester. The enantiomeric excesses for cis-olefins and terminal olefins are not high yet. The current epoxidation shows that the catalyst efficiency is enhanced dramatically upon raising the pH. Mechanistic studies show that the epoxidation mainly proceeds via a spiro transition state, which provides a model for predicting the stereochemical outcome of the reaction. The planar transition state is likely to be the main competing pathway. The extent of the involvement of the planar mode is subject to the steric effect of the alkyl groups on the olefins.

Structural Probing of D‐Fructose Derived Ligands for Asymmetric Addition of Diethylzinc to Aldehydes.

“…6 Thus, the pyridyl alcohols 2a and 2b and bromopyridyl alcohols 7 could be prepared easily in moderate yields by monolithiation of 2-bromopyridine and 2,6-dibromopyridine in ether at −78°C followed by treatment with chiral ketones 1a and 1b (Scheme 2). The optically active C 2 -symmetrical bipyridyl alcohols 5a and 5b were then prepared via Ni(0)-mediated homocoupling 7 in 52-55% yields.…”

“…D-Fructose is readily available and its derivatives 1a and 1b could be readily prepared 6 (Scheme 1). With the aim of improving their performance and widening their use as ligands in asymmetric catalysis, we report herein the synthesis of chiral ligands 2-6 derived from D-fructose and their application as catalysts in the enantioselective addition of diethylzinc to aldehydes.…”

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications

“…T he reaction of sulfur ylides with carbonyl compounds to give epoxides (1-8) provides a complementary method with oxidation of alkenes (9)(10)(11)(12) for the preparation of these valuable synthetic intermediates. Although sulfur ylide reactions have traditionally operated with stoichiometric amounts of sulfonium salts, we have recently reported a user-friendly, catalytic, and asymmetric process for epoxidation of carbonyl compounds that operated under neutral conditions by using tosylhydrazone sodium salts as diazocompound precursors and substoichiometric amounts (5 mol% in many cases) of chiral sulfide 1 and metal catalyst (Scheme 1) (13)(14)(15)(16).…”

Síntese da Epoxone a partir de D-frutose: um experimento didático em laboratório de Química Orgânica com foco nos princípios da Química Verde

“…Os métodos descritos na literatura para dicetalização da D-frutose (2) envolvem a utilização de acetona (geralmente na presença de 2,2-dimetoxipropano) sob catálise ácida, com rendimentos na faixa de 33-53%. [19][20][21][22][23] Optou-se por uma combinação que inclui apenas acetona e ácido sulfúrico, 20 devido à facilidade de aquisição e manipulação destes reagentes (Esquema 2). A reação é extremamente simples e, ao contrário do descrito na literatura para a utilização de ácido perclórico como catalisador, 19,22 foi realizada sem a necessidade de atmosfera inerte, o que viabiliza a aplicação extensiva em aulas experimentais na maioria dos cursos no país.…”

“…Além disso, as condições descritas incluem a necessidade de conduzir ambas as etapas reacionais sob atmosfera inerte, o que é inviável em laboratórios que não dispõem de infraestrutura adequada. Desta forma, decidiu-se revisar as metodologias previamente descritas na literatura para a preparação de 1 a partir de 2 [20][21][22][23][24][25] e, de modo a desenvolver experimentos compatíveis com as condições existentes em nossos laboratórios de ensino, optou-se pela substituição de ácido perclórico e de PCC por reagentes alternativos.…”