Ring-opening reactions of oxirane

Whereas the thermal ring-opening reaction of oxiranes and aziridines is frequently used for generation of carbonyl ylides and azomethine ylides, the analogous procedure starting with thiiranes does not produce the expected thiocarbonyl ylides (8). However, in the case of tetraaryl-substituted thiiranes, the photolytically mediated reaction with tetracyanoethylene (TCNE) is believed to occur via a single electron transfer (SET) mechanism, also involving a thiocarbonyl ylide as a likely intermediate (75,76) (Scheme 5.14). 

The mechanisms and the regio- and stereo-selectivity of epoxide reactions have been reviewed.39 The review also covers the role of epoxides in biologically important reactions. The achiral and chiral catalysts used in these reactions are discussed. A second review40 discusses the ring-opening reactions of oxiranes with carbon nucleophiles. 

Azides are excellent nucleophiles for the ring-opening reactions of oxiranes (Scheme 42) <1995CC1021>. 

Furthermore, in respect to the regioselectivity of the ring opening reaction of oxiranes, electronic as well as steric factors can play a role. These general considerations stimulate the use of zeolites and non zeolitic molecular sieves as heterogeneous catalysts for such rearrangement reactions in the liquid or in the gas phase in a slurry reactor and in a continuous fixed bed reactor, respectively. 

Azides are excellent nucleophiles for the ring-opening reactions of oxiranes. Ytterbium triisopropoxide, prepared in situ from Yb(OTf)3 and LiOr Pr in THF, can be used in a very mild, highly efficient, and widely applicable procedure for the azidolysis of epoxides (Equation 19) <1995CG1021>. 

Copper-catalyzed enantioselective allylic alkylation ring-opening reactions of oxiranes (and aziridines) with alkyl metals (e.g., dialkylzincs) has been reviewed by Pineschi <2004NJC657>. 

Organolithium compounds are less reactive than lithium organocuprates. A number of publications deal with the differences observed between the two reagents in the ring-opening reaction of oxiranes. The reaction of 1,3-cyclohexadienemonooxirane with methyllithium is seen in Eq. 277. ... 

Consult [4] and compare other ring-opening reactions of oxiranes, e.g. the p-cyclodextrin-catalyzed aminolysis [5] and problem 3. For an enantioselective ring-opening of oxiranes utilizing the JACOBSEN catalyst (problem 1) see [6]. 

Nucleophilic Ring-opening Reactions of Oxirans.—Reactions with Oxygen and Nitrogen Nucleophiles. A series of papers have appeared that deal with the reactions of lower aliphatic alcohols (R OH) with (120 = Me) to yield (121 ... 

A novel ring-opening reaction of oxirans, catalysed by copper and pyridine, generates c/s-diols under mild conditions. The bicyclic epoxides (186 = 1 or 2) yield (187 n = 1) (95%) and (187 = 2) (85%) in neutral, phosphate-buffered, solution. This type of reaction may have some relevance to the metabolic pathways for fused aromatic compounds, which are thought to proceed via arene oxides and diol epoxides. The catalyst system may be used to add OH", Cr, or MeO regiospecifically to the benzylic centre of indene oxide, with proton addition to the oxygen atom of oxiran. 

Scheme 6 Ring-opening reaction of oxirane group.

Tdvalent lanthanides are used with Amberlyst 15 in a variety of organic reactions requiring hard Lewis acid catalysts. These conditions can be used for aza- Diels-Alder reactions, transacetali-zations, ring-opening reactions of oxiranes with nucleophiles, and as a promotor in glycosylations of glucosyl fluorides in methanol. The ytterbium-mediated Mukaiyama aldol reaction of a silyl enol ether with formaldehyde can be conducted in aque ous THF solution with paraformaldehyde (eq 12). Lanthanide (III) catalysts supported on Amberlyst 15 and Amberlyst XN-1010 are more effective catalysts compared to other exchange resins. 

Jary s group have prepared 4,6-dideoxy-D-araftwo-hexose, 3,4,6-trideoxy-D-erythro- and -n-threo-hexose, and 2,4,6-trideoxy-D-ery/Aru-hexose by conventional ring-opening reactions of oxirans. New syntheses of 2,3,6-trideoxy-DL-ery/Aru-hexose (oL-amicetose) and 2,3,6-trideoxy-L-/ eu-hexose (rhodinose) (Scheme... 

The literature describes numerous active pharmaceutical ingredients where the synthesis uses the ring opening reaction of oxiranes or aziridines with organic or inorganic azides. Two well-known examples of commercial-scale application shall be mentioned here. 

KCIO4 and KBF4 do not exert any catalytic activity for aminolysis of oxiranes. Totally, LiCl04 seems to be the most prominent and general reagent for the ring opening reaction of oxiranes with a nucleophile. 

N2-Type processes are involved in the ring-opening reactions of oxirans, under mild conditions (by thiols, adsorbed on alumina), and in the ring-closure of a penicillin-derived enethiolate. ... 

Two reviews, one discussing the mechanisms of the Lewis acid-catalysed ring-opening reactions of fiillerene epoxides by nucleophiles and the other covering the ring-opening reactions of oxiranes and aziridines in water, have been published. 

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