Mechanistic evidence for remote pi-aryl participation in acid-catalyzed ring opening of homobenzoquinone epoxides

The acid-induced reaction of bis(p-chlorophenyl)homobenzoquinone epoxide gave the dual ipso/ortho intramolecular S(E)2-Ar products associated with pi-aryl participated oxirane ring opening, whereas bis(p-tolyl)- and diphenyl-substituted homologues provided only the ortho products.     

Conformational effects in acid-mediated ring opening of epoxides: a prominent role of the oxirane Walsh orbital

A kinetic study has been made of the BF(3)-mediated ring opening of two rigid conformers (alpha and beta) of m- and p-dimethyl-substituted homobenzoquinone epoxides spiro-linked with a twist-boat dibenzocycloheptene ring as compared with the conformationally mobile epoxides bearing diphenyl groups. The rates of the regioselective ring opening were dependent on the topological alignment of the dibenzocycloheptene ring as well as the substitution pattern of the quinone dimethyl groups, indicating pi-aryl participated orbital interaction with the vacant Walsh orbital of the oxirane ring.     

Rhodium-catalyzed ring opening of vinyl epoxides with alcohols and aromatic amines

[Rh(CO)(2)Cl](2) is an effective catalyst for the ring opening of vinyl epoxides with alcohols and aromatic amines under neutral conditions at room temperature. The reaction occurs with excellent diastereo- and regioselectivity (>20:1) giving the trans-1,2-amino alcohols or alkoxy alcohols for a wide range of substrates. The regio- and stereochemistry of these reactions is complementary to that typically obtained with palladium-catalyzed ring openings of vinyl epoxides.     

Allyltin tribromide: A versatile reagent involved in the ring-opening of epoxides

This paper presents a versatile reagent for epoxide cleavage. The allyltin tribromide could act as a novel and easily prepared allylation reagent and halide atom donor to convert epoxides to the corresponding homoallyl alcohols and halohydrins in high yields with excellent regioselectivities under mild reaction conditions, respectively. It could also act as a Lewis acid to catalyze the ring opening reactions of epoxides with alcohols.     

Hydrazine sulphate: a cheap and efficient catalyst for the regioselective ring-opening of epoxides. A metal-free procedure for the preparation of β-alkoxy alcohols

An efficient and general procedure for the regioselective ring opening of epoxides with alcohols to afford the corresponding β-alkoxy alcohols, using hydrazine sulphate as catalyst, is described. This new metal-free process was found to be highly versatile allowing the use of primary, secondary and tertiary alcohols as nucleophiles and a large variety of epoxides, including 5α,6α-, 5β,6β- and 2α,3α-epoxysteroids, as substrates.     

锆氢化反应研究 VI:环氧化合物的选择还原

环氧化合物还原成醇,是较为常见的反应。其区域选择性取决于所使用的还原剂。一般规律是:LiAlH_4类型的亲核性复合金属氢化物从空间障碍较小的部位接近氧,从而获得取代基较多的醇;而硼烷(尤其在BF_3存在之下)或铝烷类型的亲电性金属氢化物则使环氧化合物从相反方向开环并主要获得取代基较小的醇。锆氢试剂(Cp_2ZrHCl)对羰基化合物的还原已经详细研究,本文将研究环氧化合物的还原及其区域选择性,并进一步认识锆氢试剂在反应中的作用及其本质。     

Highly regioselective ring opening of epoxides with alcohols catalyzed by organotin phosphate condensates

Organotin phosphate condensates proved to catalyze the ring opening reaction of epoxides with alcohols in a highly regioselective manner.     

Nucleophilic Difluoromethylation of Epoxides with PhSO(NTBS)CF2H by a Preorganization Strategy

Unlike the facile synthesis of β‐monofluoromethyl alcohols by nucleophilic monofluoromethylation of epoxides, the synthesis of β‐difluoromethyl alcohols by nucleophilic difluoromethylation of epoxides still remains a challenge. Herein, studies on tackling this problem with PhSO(NTBS)CF₂H ( 2 ; TBS=tert‐butyldimethylsilyl) are reported. The preorganization of 2 and epoxides with BF₃ ? Et₂O was found to be crucial for the reaction. The reaction shows excellent regioselectivity and has a broad substrate scope. The facile transformation of the ring‐opened products to β‐difluoromethyl, γ‐difluoromethyl, and β‐difluoromethylenyl alcohols demonstrates the synthetic utility of the reaction.     

Bismuth triflate-catalyzed mild and efficient epoxide opening by aromatic amines under aqueous conditions

Bismuth triflate catalyzes the ring opening of epoxides with aromatic amines under aqueous conditions. The reaction proceeds rapidly and affords the corresponding β-amino alcohols in excellent yields.     

Aluminium triflate: a remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols

Al(OTf)3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols.     

Enantioselective ring opening of epoxides with trimethylsilyl azide (TMSN3) in the presence of β-cyclodextrin: an efficient route to 1,2-azido alcohols

The ring opening of epoxides with nucleophiles such as TMSN₃ and isopropylamine takes place enantioselectively in the presence of β-cyclodextrin under extremely mild conditions and the azido alcohols and amino alcohols are formed as (S)-isomers.     

Ferric Perchlorate: An Efficient Reagent for Regio- and Stereoselective Alcoholysis and Hydrolysis of Epoxides

Regio- and stereoselective ring opening reaction of epoxides is achieved efficiently by aliphatic alcohols and water in the presence of catalytic amounts of ferric perchlorate.     

A facile and efficient synthesis of β-amino alcohols using 2,2,2-trifluoroethanol as a metal-free and reusable medium

Trifluoroethanol was used as a reusable catalyst and medium for the ring opening of epoxides using aliphatic and aromatic amines as nucleophile under mild conditions to give the corresponding β-amino alcohols in high yields and regioselectivity.     

Rapid Ring‐Opening Reactions of Epoxides using Microwave Irradiation

Copper tetrafluoroborate catalyzes the ring‐opening of epoxides with primary, secondary, and tertiary alcohols in short reaction times under microwave irradiation to give β‐alkoxyalcohol products in excellent yields.     

2-Amino homopropargyl alcohols from the highly regioselective Ag2CO3-catalyzed nucleophilic openings of alkynyl epoxides by amines

The nucleophilic ring opening of propargyl epoxides by amines based on a silver catalyst is presented. The reaction takes place under mild conditions and features a high regioselectivity to provide an effective method for the synthesis of 2-amino homopropargyl alcohols in moderate to high yields.     

Graphene oxide as an acid catalyst for the room temperature ring opening of epoxides

The minute amount of hydrogen sulfate groups introduced into the graphene oxide (GO) obtained by Hummers oxidation of graphite renders this material as a highly efficient, recyclable acid catalyst for the ring opening of epoxides with methanol and other primary alcohols as nucleophile and solvent.     

Regioselective nucleophilic opening of epoxides and aziridines under neutral conditions in the presence of β-cyclodextrin in water

A variety of β-hydroxy nitriles and β-amino alcohols have been synthesized by the regioselective ring opening of epoxides and aziridines under neutral and aqueous conditions in the presence of β-cyclodextrin in good yields.     

Mild,Efficient and Selective Opening of Epoxides with Alcohols Catalyzed by Ceric(IV) Ammonium Nitrate

Commercially available Ceric(IV) Ammonium Nitrate (CAN) catalyzes nucleophilic ring opening of epoxides in primary, secondary and tertiary alcohols under mild conditions. The corresponding β-alkoxy-alcohols were obtained with high regio and stereoselectivity in high yields.     

A practical one-pot radical-ionic sequence for the preparation of epoxides: application to the synthesis of unnatural polyhydroxylated alkaloids

An efficient one-pot sequence for the preparation of epoxides from α-iodoesters or α-iodonitriles and allylic alcohols is described. This sequence is based on the use of iodine atom transfer reaction onto allylic alcohols followed by a ring closing epoxidation reaction of the halohydrin intermediates. The feasibility of this sequence is showcased in the synthesis of the perhydroaza-azulene, an unnatural analog of castanospermine.     

Antimony(III) chloride-catalyzed ring opening of epoxides with anilines

A mild and convenient ring opening of epoxides with aniline and its derivatives takes place at room temperature in the presence of antimony trichloride as catalyst to afford the corresponding β-amino alcohols in good yields.