Recent advances in the preparation and synthetic applications of oxiranes

Functionalization of epoxy esters with alcohols as stoichiometric reagents

“…Ring strain, polarity of C-O bond and basicity of oxygen atom make them substantially reactive and thus suitable intermediates for transformation to other classes of compounds. [1][2][3][4] The most extensively employed reaction of epoxides is a nucleophilic attack to one of ring carbons, accompanied by ring opening. C, N, P, O, S and halogen nucleophiles comprise the most important reagents for achieving such transformations.…”

Diastereo- and enantioselective syntheses of heteroaryloxiranes

“…1 An interesting diastereoselectivity has been observed in the coupling reaction of the above carbanions with carbonyl or iminic compounds affording oxiranes and aziridines, respectively. 2 The option of deblocking the oxiranyl ring 3,4 as well as the potential elaboration of the aza heterocycle to a carbonylic function, make these compounds extremely useful intermediates in the organic synthesis of biologically active compounds. 5 It has been reported that the coupling reaction of lithium azaenolates of chiral oxazolines with carbonyl compounds 6 produces asymmetric induction leading to chiral oxiranes.…”

“…Moreover, the deprotonation of substituted oxazolinyloxiranes with strong bases has been reported, affording oxiranyl anions chemically and configurationally stable to react stereospecifically with electrophiles; 7 recently the coupling The coupling reaction can occur by two possible attacks of the carbanion to the electrophile affording four possible diastereoisomers. According to the route α, a carbanion attack of anti type towards the cyclohexanic CH 3 should take place leading to the diastereomers a (trans configuration) and b (cis configuration). An attack of syn type, as showen by the route β, should produce diastereoisomers c (trans configuration) and d (cis configuration).…”

“…The trans and cis relative configurations for all the above compounds were assigned in comparison with the structure (+)-2a, which was assigned by X-ray measurements, and considering also the oxiranic oxygen atom and the heterocycle influence on the chemical shift of the cyclohexanic CH 3 . An heteroatom having a lone pair deshields the protons lying in the Van der Waals radius, therefore the δ CH3 of the structures a and b is always bigger than that showed by the structures c and d, having, these latter, the farthest oxygen atom.…”

Crystal structure of (6R ,7S)-N-benzhydryl-6-hydroxy-7-methyl- 2-tert-butyl-4,5,6,7-tetrahydro-4-aza-oxepin-5-one, C23H27NO3

“…Such acyclization process is allowed by the Baldwin's rules [5], but the occurrence of seven-membered rings from intramolecular epoxide ring-opening appears rather low [3,6,7]. …”