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.     

Synthesis of allylic alcohols from oxazolinyloxiranes

Lithium diisopropylamide (LDA) (or s-BuLi/TMEDA) in diethyl ether promotes smooth ring opening of oxazolinyl alkyl oxiranes to give oxazolinyl allylic alcohols, which are masked Baylis-Hillman adducts, in good to excellent yields. An E2-E1cb-like syn-beta-elimination is proposed to explain the easy base-promoted isomerization of the studied oxiranes.     

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.     

A stereospecific synthesis of oxazolinyloxiranes

Lithiooxiranes 3a and 3b, generated by deprotonation of oxiranes 2a and 2b with s-BuLi at -100 degrees C in Et(2)O, were found to be chemically very stable. trans-Lithiooxirane 3a was also configurationally stable and reacted stereospecifically with electrophiles to give 4a--k. In contrast, cis-lithiooxirane 3b was found to be configurationally much less stable and reacted with electrophiles affording mixtures of diastereomers 4, 7, and 8. After only a very short reaction time, 3b too reacted with electrophiles highly stereospecifically. Deprotonation--deuteration and deprotonation--alkylation of chiral oxazolinyloxiranes 12a and 12b to give oxiranes 12c and 12d were also examined. Semiempirical and ab initio calculations were carried out in an effort to explain the observed stereochemistry.     

Stepwise conversion of oxiranes to allylic alcohols by iodotrimethylsilane and DBU

Iodotrimethylsilane, prepared from hexamethyldisilane and iodine reacts smoothly with oxiranes to give (2-iodoalkoxy)trimethylsilanes which can be converted to allylic alcohols with DBU in good yields. The whole conversion can be carried out in one-pot operation.     

Formation of 1,2-dioxolanes using Mn(III)-based reaction of various arylacetylenes with 2,4-pentanedione and related reaction

The manganese(III)-based aerobic oxidation of arylacetylenes with 2,4-pentanedione at ambient temperature unexpectedly gave the 1,2-dioxolane derivatives in moderate yields together with a small amount of the oxiranes. The 1,2-dioxolanes underwent silica gel-assisted contraction to quantitatively give the oxiranes. The reaction pathway for the formation of the 1,2-dioxolanes and the by-product was discussed.     

Reaction of Oxiranes with Ethyl 3-Phenyl-1H-pyrazole-5-carboxylate

Russian Journal of Organic Chemistry - Ethyl 3-phenyl-1H-pyrazole-5-carboxylate reacted with oxiranes to give mixtures of 2-phenyl-6-R-6,7-dihydro-4H-pyrazolo[5,1-c][1,4]oxazin-4-ones and ethyl...     

Nucleophilic epoxidation of alpha'-hydroxy vinyl sulfoxides

The nucleophilic epoxidation of a variety of alpha'-(1-hydroxyalkyl) vinyl sulfones and sulfoxides has been studied. The sulfones give rise to anti oxiranes with modest (E) or excellent (Z) selectivities and in good yields. The (E)-sulfoxides display low reactivity within a reinforcing/nonreinforcing scenario. The use of t-BuOOLi in Et(2)O allows for a highly syn-selective epoxidation-oxidation. The (Z)-sulfoxides display a remarkably high reactivity under these conditions. The reinforcing (S,S(S)) diastereomers (3e-g) yield hydroxy sulfinyl oxiranes with high yields and selectivities. In contrast, the (R,S(S)) diastereomers (4e-g) show diminished reactivities and a very substrate-dependent stereochemical outcome. The structure of these oxiranes has been secured by chemical correlations and an X-ray crystal structure.     

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.     

The reaction of lithium trialkylalkynylborates with oxiranes : γ-Hydroxyketone synthesis and stereoselective preparation of trisubstituted ethylenes

Lithium trialkylalkynylborates (1) react with oxiranes (2) to give non-isolable intermediates 3 which subsequently afford either γ-hydroxyketones 5, trisubstituted ethylenes of homoallylic alcohol type 6 or a tetrasubstituted ethylene 7 upon appropriate treatment with NaOH/H₂O₂, AcOH or NaOH/I₂, respectively. The reaction of oxiranes with 1 proceeds in high regioselectivity and the resulting homoallylic alcohols 6 are of nearly 100% (E) configuration. A straight chain γ-hydroxyketone 16 is obtained in the reaction of methyloxirane with the ate-complex (1), which has been prepared from lithium acetylide ethylenediamine complex and trihexylborane.     

First chiral selenium ylides used for asymmetric conversion of aldehydes into epoxides

Enantioenriched selenonium ylides have been generated by addition of benzyl bromide to C2 symmetric (2R,5R)-2,5-dimethylselenolane in the presence of NaOH, and subsequently reacted with a variety of aldehydes to give oxiranes with excellent enantiomeric excesses (a catalytic version has been achieved); also, an aliphatic cyclic hypervalent dibromoselenurane structure has been demonstrated by X-ray analysis.     

Corrigendum

Prochiral α-haloketones are reduced enantioselectively with the asymmetric reducing system lithium borohydride N,N′-dibenzoylcystine /t-butyl alcohol to give the corresponding halohydrins with up to 86% enantiomeric excess, some of which are converted to optically active oxiranes.     

Stereoselective generation of cis-2-lithio-3-CF3-oxirane via CF3-substituted β-oxido carbenoids. Highly stereoselective synthesis of CF3-substituted tri- and tetrasubstituted oxiranes and tetrasubstituted alkenes

Treatment of 2-substituted 3,3-dichloro-1,1,1-trifluoropropan-2-ols with organolithium reagents R²Li in THF at −98°C stereoselectively produces 2,3-disubstituted 2-lithio-3-trifluoromethyloxiranes with Li and CF₃cis. The reagents react with electrophiles El-X or organoboranes R³BR₂ to give CF₃-containing tri- and tetrasubstituted oxiranes or tetrasubstituted alkenes, respectively, with high diastereoselectivities.     

The dimesitylboron group in organic synthesis 8. Preparations of 1,3-diols from oxiranes

Alkyldimesitylboranes, yield anions¹, Mes₂B$\text{C}$HR, that on reaction with oxiranes followed by oxidation give 1,3-diols. These anions are thus the operational equivalent of R$\text{C}$HOH. The scope and limitations of the new process are delineated.     

Zwei neue reaktionsweisen von alkyl-Mn(II)-verbindungen: 1,4-addition an cyclohex-2-enon(1) und desoxygenierung von oxiranen (1)

Alkyl Mn(II) compounds react like alkyl Cu(I) compounds specifically or highly selectively with cyclohex-2-enone(1) to give 3-alkylhexanones (Alk  Me, Bu) in medium or good yields. By reacting with oxiranes corresponding alkenes are produced, a reaction not observed so far with alkyl Cu(I) reagents.     

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.     

Double deprotonation of acetylenic oxiranes: synthesis of allenic ketones through Dilithio Ynenolates

[reaction: see text] The double deprotonation of acetylenic oxiranes gives allenic ketones through the 1,2-H or 1,2-Ar shift on the transient oxiranyl dianion intermediates. The resulting dilithium ynenolates give allenic ketones upon hydrolysis or can be quenched with various electrophiles.     

Synthesis of some sulfonium salts and ylides containing the isoxazole nucleus

Some dimethylisoxazolylmethylsulfonium salts and the corresponding ylides were synthetized and their chemical behaviour studied. Dimethylsullonium-5-isoxazolyl methylides (XIa,b) give 5-isoxazolyloxiranes (XIIa,d) and XIII when allowed to react with carbonyl compounds. Ring opening products from these oxiranes are also reported.