Oxirane ring expansion

Benzopyran 160 reacts with 2,3-dichloro-l, 4-naphthoquinone by substitution of both chlorine atoms. The unstable primary adduct 161 undergoes ring expansion of oxirane 162 to produce thieno benzoxipine 163 in 70% yield (Scheme 32 (1994JCS(P1)2191)). 

This heterocycle has been reported to result from a ring expansion reaction of a pendant oxirane with a ketone (75MI11107). The insertion reaction (Scheme 100) was conveniently conducted in high yield by treatment of a solution of a glycidyl methacrylate-containing polymer (208) employing the ketone as solvent. 

Oxiranes and oxetanes with ether substituents in side chain undergo ring expansion in the presence of BF3-OEt2. Selecting the appropriate side chain, this ring expansion of oxetanes, for example, 107, gives oxepane 108 (Equation 39) in medium yield <1994H(38)2165>. 

Whereas bis(triphenylphosphane)platinaaziridine 181 reacts readily with HFA, the corresponding oxirane is inert toward ring expansion. This may be explained in terms of stronger n acceptor and weaker a donor capacity of... 

Gree and co-workers have found that bicyclic epoxy alcohols when treated with diethylamino sulfur trifluoride (DAST) can undergo a ring expansion via C-C bond cleavage of the oxirane ring to provide fluorinated cyclic vinyl ethers (Table 17) <20020L451>. 

The main products formed from the oxiranes 107 and 108 on the action of BF3 are the corresponding ketocyclopropane isomers in addition, however, with doublebond participation and ring expansion, 109 is also obtained.Similar transformations have been observed in the cases of 110 and 111 as well. ... 

Cu(hfacac)2-catalyzed elimination of N2 from aroyl(a-diazoacyl)hydra-zines 653 yields 2//-l,3,4-oxadiazin-2-ones 654 (70%). The reaction occurs consecutively via intramolecular carbonyl ylide formation, 1,3-cyclization into oxirane 655, and ring opening by the carbon-oxygen bond followed by a C- 0 shift with ring expansion (88CB887). 

Acetates can be used instead of alkenes. Cyclic ketones undergo ring expansion to give a-hydroxyketone precursors. Oxiranes ring-open with siloxymethylation at ambient temperature and CO pressure. ... 

Keywords SN2 and SN2 reactions Baldwin mles Oxirane opening Activation of a cyclopropane 1,2-rearrangement Ring contraction Ring expansion Solvolysis Neighboring group participation Oxirane rearrangement Classical and nonclassical carbocations 5-exo- vis-a-vis 5-endo cyclization Addition and elimination reactions... 

The mechanism for the gas-phase reaction of trans-2,3-dideuterioethene oxide with HBr and HCl has been shown to involve anti ring-opening, with the formation of e fhro-R(CHD)2 0H (R = Cl or Br). The reaction of ethene oxide with HF followed a somewhat different course, affording only 5% of fluorohydrin together with (126) (37%) and oligomers and polymers. A possible mechanism for this reaction is shown (see Scheme 8) in which two moles of oxiran react with HF to give intermediate (125), which is open to polymerization with other oxiran molecules or to ring-expansion, with the subsequent formation of dioxane (126). 

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