杂多酸引发四氢呋喃开环聚合反应Ⅶ.以氧杂环丁烷为促进剂

在以低浓度杂多酸(HPA)催化四氢呋喃(THF)聚合反应中,我们曾采用环氧乙烷(EO)、环氧丙烷(PO)和环氧氯丙烷(ECH)等三元环醚为促进剂,发现它们对聚合反应都具有很好的促进效果[1～3]. 本文进一步研究了具有四元环醚结构的氧杂环丁烷(OX)对THF聚合的促进效果.     

Stereospecific cycloaddition of heterocumulenes to oxiranes catalyzed by organotin halide complexes

Stereospecific cycloaddition of 2,3-disubstituted oxiranes to heterocumulenes, including carbodiimides, isocyanates and carbon dioxide, is catalytically promoted by dialkyltin diiodide-hexamethylphosphoric triamide (HMPA) system, producing various five-membered heterocycles, where the configuration of the carbons in the oxirane ring is retained. In particular, the addition of isocyanates to oxiranes gave stereo-specifically two types of products, dioxolan-2-imines and oxazolidin-2-ones independently, while the rearrangement of the former to the latter product has been already proposed.     

Selective α-cleavage cycloaddition of oxiranes with heterocumulenes catalyzed by tetraphenylstibonium iodide

A catalytic amount of tetraphenylstibonium iodide ( 1 ) promoted unusual cycloadditions of oxiranes with isocyanates or carbodiimides, forming 3,4-disubstituted oxazolidin-2-ones 2 and oxazolidin-2-imines 4 under very mild conditions, respectively. In particular, carbodiimides gave 4 exclusively. Either oxazolidine, 3,4-disubstituted or 3,5-disubstituted ones could be obtained independently from the same reactants by the compensatable use of 1 and organotin iodide-Lewis base complexes as catalysts.     

Regio- and Stereoselective Formation of 1,3-Oxathiolanes by Reactions of Thiocarbonyl Compounds with Oxiranes

Abstract

Lewis acid-catalyzed reactions of oxiranes with a variety of C═S compounds yield 1,3-oxathiolanes. The ring enlargement of monosubstituted oxiranes occurs regioselectively via cleavage of the O,C(3) bond of alkyl substituted oxiranes and the O,C(2) bond of phenyl oxirane. Furthermore, the reaction proceeds with inversion of the configuration at the center of the nucleophilic attack by the S-atom. The formation of thiocarbonylium ions as intermediates is supported by Wagner–Meerwein-type rearrangements. Enolized thioketones react with oxiranes to give enesulfanyl alcohols, which undergo an acid-catalyzed cyclization to yield 1,3-oxathiolanes.     

A facile method for the synthesis of 1,3-oxathiolan-2-ones by reaction of oxiranes, sulfur, and carbon monoxide

A new method for the synthesis of 1,3-oxathiolan-2-ones has been developed. When oxiranes were allowed to react with sulfur in the presence of a catalytic amount of sodium hydride under pressurized carbon monoxide, the three-component coupling of oxiranes, sulfur, and carbon monoxide smoothly proceeded to give the 1,3-oxathiolan-2-ones in moderate to good yields. The reaction proceeded with a high regioselectivity and stereospecificity. For the reaction of oxiranes possessing an aromatic ring, the yields of the 1,3-oxathiolan-2-ones were lower than that of the oxiranes possessing no aromatic ring due to the formation of alkenes and thiiranes as byproducts. However, the product yields were improved by the addition of a catalytic amount of selenium.     

Nucleophilic epoxidation of γ-alkoxy dienyl sulfoxide derivatives

(E,E) and (Z,E) γ-alkoxy dienyl sulfones undergo nucleophilic epoxidation with remarkable regio- and stereoselectivity to render syn oxiranes in a process mainly controlled by the alkoxy stereocenter. Upon epoxidation γ-hydroxy dienyl sulfoxides provide sulfinyl and sulfonyl oxiranes along with bis-epoxides formed through a Payne rearrangement that can be prevented by silylation of the OH group. Interestingly, the presence of a γ-silyloxy group can invert the stereochemical trend of the molecule affording mainly an anti epoxidation process.     

Enantioselective Darzens reaction using organoselenide-lithium hydroxide complexes

Asymmetric Darzens reaction catalyzed by chiral selenides is described. A novel Lewis acid/Brønsted base catalyst formed by C₂ symmetric chiral selenide-bearing isoborneol skeletons, which were readily prepared from (1S)-10-camphorsulfonic acid, and LiOH promoted the reaction of phenacyl bromide with aldehydes to afford the desired trans oxiranes with up to 62% ee.     

Ionic Pathways in the Photochemistry of Cyclic Sulfite Esters

The photochemistry of cyclic carbonate esters proceeds by the photochemical extrusion of carbon dioxide to give 1, 3‐diradicals which produce oxiranes as well as other radical derived species. The corresponding cyclic sulfite esters, upon irradiation, give intermediates that are trapped by alcohols yet generate no oxiranes. These results are consistent with ionic intermediates.     

Copper Salt Catalyzed Synthesis of Functionalized 2H‐Pyranes

A copper‐catalyzed reaction between terminal alkynes, oxiranes, and malonitrile has been described. In this transformation, copper acetylide was attacked on oxiranes to form homopropargyl alkoxy‐copper intermediate that was further transferred to 2H‐pyrane skeletons by reaction with malonitrile. We found that the reaction was not productive without hexafluoroisopropanol.     

Remarkable selectivity in addition of alcohols to epoxydienes of 5,7 bicyclic and 5,7,6 tricyclic systems

Acid-catalyzed addition of alcohols to tricyclic dienyl epoxides such as 4 or bicyclic vinyl oxiranes such as 17 exclusively occurred at the vinyl terminus of unsaturated system through a typical S(N)2' process affording 1,6- and 1,4-dioxygenated derivatives, respectively.     

A catalytic synthesis of dihydrofuran-3(2H)-imine skeletons from isocyanides,terminal alkynes,and oxiranes

In this catalytic multicomponent reaction, the nucleophilicity of terminal alkynes and isocyanides towards oxiranes has been explored. The reaction outcome depends highly on solvent, bases, and catalysts sources. An array of terminal alkynes, isocyanides, and oxiranes has been examined to explore the of this transformation. The reactions proceeded through S_N2 path and in regioselective manner.     

Photoinduced fragmentation and rearrangement of phenyl substituted epoxyethylphosphonates

An alternative source to phosphonocarbenes is described using phosphorus substituted oxiranes as precursors which compliments the conventional diazo route to these transient species. The results are in accord with previous theories advanced to rationalize the mode of photocyclo-elimination of a variety of other unsymmetrically substituted oxiranes.     

The polymerization of oxiranes with the α-chlorobenzyl methyl sulfide–antimony pentachloride initiator system

α-Thiomethoxyphenylmethylium hexachloroantimonate was prepared from α-chlorobenzyl methyl sulfide and antimony pentachloride and studied by visible spectroscopy. The salt is unstable at room temperature and used as in situ initiator for the polymerization of oxiranes in dichloromethane. Propylene oxide (PO) and cyclohexene oxide (CHO) were used as oxiranes. The microstructure of PO polymer is amorphous by ¹³C-NMR. The initiator was more effective for the polymerization of CHO than for that of PO.     

Reaction of optically active alpha-aminoallenylstannanes with aldehydes formed in situ from the Lewis-acid-catalyzed rearrangement of epoxides

Reaction of optically active alpha-oxazolidinonylallenylstannanes with oxiranes in the presence of BF3.OEt2 produced beta-hydroxypropargylamines with high syn diastereoselectivity and high enantioselectivity through an initial Lewis-acid-catalyzed rearrangement of the oxirane to the corresponding aldehyde via an alkyl, aryl, or hydride shift. This permits the use of readily available oxiranes as alternatives to aldehydes that are difficult to prepare and/or unstable.     

非对称环氧乙烷的区域选择性亲核开环反应

本文总结了常用亲核试剂对非对称环氧乙烷的亲核开环反应及其区域选择性。强亲核性的亲核试剂通常只受空间效应影响,进攻非对称环氧乙烷位阻小的碳原子,对于烯基取代环氧乙烷还可以进攻烯基的β-碳原子发生S_N2'开环反应,其他亲核试剂同时受空间效应和电子效应的影响,对于烷基环氧乙烷通常进攻其取代少的碳原子, 空间效应起主导作用,而对芳基和烯基取代环氧乙烷开环反应通常发生在环氧乙烷芳甲位和烯丙位的碳原子上, 电子效应起主导作用。在质子酸或强Lewis酸存在下,虽然单烷基环氧乙烷的开环仍然发生在其取代少的碳原子上,但对于芳基、烯基和同碳双取代环氧乙烷,亲核开环反应将主要受电子效应控制,一般亲核试剂倾向于进攻环氧乙烷的芳甲位、烯丙位或多取代的碳原子。分子内的亲核开环反应主要受成环时环大小的控制, 成环时的倾向是五元环> 六元环> 七元环。环氧乙烷亲核开环的区域选择性是环氧乙烷和亲核试剂空间效应和电子效应平衡的结果。     

Iodine as a mild, efficient, and cost-effective catalyst for the synthesis of thiiranes from oxiranes

We developed an efficient protocol for the synthesis of thiiranes from oxiranes using a catalytic amount of molecular iodine. The notable features of this procedure are mild reaction conditions, high conversions, short reaction times, economic viability of the reagents, compatibility with various functionalities, and simple experimental/product isolation procedures which make it a useful and attractive process for the synthesis of a range of thiiranes.     

Synthesis, spectral studies, antimicrobial, antioxidant and insect antifeedant activities of some 9H-fluorene-2-yl keto-oxiranes

Thirteen ee (αS, βR) 9H-fluorene-2-yl keto-oxiranes (2-(9H)-fluorene-4-yl[3-(substituted phenyl)oxiran-2-yl]methanones) have been synthesized by phase transfer catalysed epoxidation of 9H-fluorene-2-yl chalcones. The yields of oxiranes are more than 95%. The synthesized oxiranes have been characterized by IR, (1)H, (13)C and GC-MS spectral data. The spectral data are correlated with Hammett substituent constants and Swain-Lupton parameters. From the regression analysis, the effect of substituents on the group frequencies has been predicted. The antimicrobial, antioxidant and insect antifeedant activities of all the synthesized oxiranes have been studied.     

Asymmetric cyclizations of some chlorohydrins catalyzed by optically active cobalt (salen) type complexes

Optically active chloromethyloxirane was obtained from 1,3-dichloro-2-propanol by a process of asymmetric synthesis. The highest enantiomenc excess (e. e. ) of chloromethyloxirane that could be obtained was 67%, using Co(II) (3,5-Cl,Cl-sal)₂(S-CHXDA) and K₂CO₃ as the catalyst and base, respectively. For purpose of comparison, asymmetric cyclizations of racemic 2,3-dichloro-1-propanol and 2-chloro-1-propanol were examined; optically active chloromethyloxirane and methyloxirane were obtained according to kinetic resolution mechanisms, although the optical purities of oxiranes formed were not so high. The mechanisms for the asymmetric reactions were investigated by circular dichroism and absorption spectroscopies. It was found that the cobalt (salen) type complex forms a new complex with alkali metal carbonate, similarly to the function of crown ether. The substrate interacts with the newly formed chiral complex, followed by cylization to give optically active oxiranes.     

Superbase-promoted rearrangement of oxiranes to cyclopropanes

Aryl- and alkenyl substituted oxiranes, when submitted to treatment with superbasic reagents, undergo a highly regio- and stereoselective rearrangement leading to cyclopropylmethanol derivatives. The process can also be applied to mono- and dihydroxy substituted substrates thus leading to polyhydroxylated cyclopropanes.     

Highly stereoselective and easy synthesis of enantiopure phosphoranyl oxiranes

The highly stereoselective synthesis of enantiopure phosphoranyl alkyl oxiranes has been accomplished by the addition of a nucleophilic stable phosphino(silyl)carbene to chiral aldehydes prepared from (−)-verbenone and d-mannitol, respectively. In the process, two new stereogenic centers are created one of them being on an oxirane quaternary carbon. The excellent π-facial diastereoselection of the aldehydes combined with the diastereoselectivity of the carbene addition allowed us to synthesize the title compounds as single stereoisomers with well defined absolute configuration.