Aryl-Substituted Oxiranes

When 2-aryl-3,3-dicyanooxiranes are reacted with aldehydes, 1,3-dioxolanes are obtained via ylide intermediates. a-Keto-a-cyanooxiranes are rearranged similarly to dioxols, but in an intramolecular process (Eq. 380).  

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Hydration of aryl-substituted epoxides. Treatment of aryl-substituted oxiranes with copper(II) sulfate and pyridine in an aqueous phosphate buffer (pH 7) affords cis-diols by reaction of water at the benzylic position. Less than 15% of trans cleavage products obtain. In the absence of pyridine, the oxides are rapidly destroyed. Triethylamine cannot be substituted for pyridine. cis-Chlorohydrins are obtained when aryl-substituted oxides are treated with copper(II) sulfate, pyridine, and kiCl in THF, When methanol is used as solvent, the corresponding cis-glycol monomethyl ether is obtained. In all cases substitution occurs at the benzylic position. Alkyl oxiranes do not react under these conditions. ... 

Oxirane has a higher boiling point (10.5°) than cyclopropane (—32.9°), which indicates its more polar character. Its dipole moment has been determined by numerous authors via the dielectric constant (e.g.. Refs. ) and the Stark effect. The results agree well 1.9D. The structures of aryl-substituted oxiranes have also been determined by means of dipole moment measurements. ... 

The kinetics of the reaction of fert-BuOK with aryl-substituted oxiranes follow a linear Taft correlation. Steroid 5a,6a- and 5(3,6/3-oxiranes react with pyridine to give 97 (Eq. 113). ... 

A fair number of publications have appeared on the isomerization of alkyl- and aryl-substituted oxiranes also containing other functional groups (e.g. Refs. " ). 

Reversed regioselectivity has been observed in reduction with lithium 9,9-di-n-butyl-9-borabicyclo[3.3.1]nonate 122. This compound reduces aryl-substituted oxiranes a to the aryl groups (in the most-hindered position) and aliphatic oxiranes in the least-hindered position (Eqs. 165 and 166). ... 

Aryl-substituted oxiranes are converted to ozonides by co-sensitized electron transfer photooxygenation with 9,10-dicyanoanthracene (DCA) and biphenyl <82CC1223,83JA663,83JA5149,83JCS596, 84JCS(P1)15>. 

A postulated mechanism for nucleophilic attack in enzymatic hydrolysis suggests that electron-withdrawing substituents on the phenyl ring must accelerate the reaction. This is seen in Table 10.1 when comparing 2-phenyl-oxirane with 2-(4-nitrophenyl)oxirane. A systematic study of a few aryl-substituted phenyloxiranes confirmed this inference [175],... 

Reaction of styrene oxide with tetraallyltin in the presence of Bi(OTf)3 (2 mol%) affords the corresponding l-phenyl-4-penten-2-ol (Fig. 5). In a similar fashion, various aryl substituted epoxides react smoothly with tetraallyltin to give the corresponding homoallylic alcohols. This method give generality as cycloalkyl oxiranes and sterically hindered ones give the corresponding homoallylic alcohols. 

Aryl- and alkenyl-substituted oxiranes, when submitted to treatment with super-basic reagents, undergo a highly regio- and stereo-selective 3-exo-cyclization leading to cyclopropylmethanol derivatives (Scheme 46). The process has be applied to mono- and di-hydroxy-substituted substrates, thus leading to polyhydroxylated cyclopropanes.78... 

Several fluorinated aryl ethers 134 were prepared from the reaction of the 11,12/3-oxirane 133 <1994TL2129> with substituted benzyl alcohols (Equation 13 Table 8) <1995JME4120>. 

AIkylthio)allylritanium reagentS, RSCH=CHCH2TiL (l).9 The reagents are prepared by deprotonation of allylic alkyl (aryl) sulfides with sec- or r-butyllithium followed by addition of Ti(0-/-Pr)4 at - 78°. They can react with carbonyl compounds at the a- or "/-position. a-Adducts predominate in reactions with a- and /1-mono- and disubstituted sulfides, whereas /-adducts predominate in reaction with /-substituted sulfides. The a-adducts show high eryr/iro-selectivity. The products are useful precursors to alkenyl oxiranes and to 2-(arylthio)-l,3-butadienes. 

Reduction with LiAlH4 is an Sjv2-type reaction " the complex anion attacks as a hydride-carrier on the side opposite to the oxirane ring if there is no steric hindrance, the ring is opened regiospecifically at the least-substituted carbon atom and yields the more-substituted alcohols. The reactivity increases in the sequence UBH4, UAIH4, and Li(sec-Bu)2BH. Examinations on optically active 1-aryl-l,2-epoxypropane and 2-aryl-2,3-epoxybutane, and 1-phenyl- and... 

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