Monosubstituted oxiranes

G. Bellucci, C. Chiappe, F. Marioni, M. Benetti, Regio- and Enantioselectivity of the Cytosolic Epoxide Hydrolase-Catalysed Hydrolysis of Racemic Monosubstituted Alkyloxiranes ,./. Chem. Soc., Perkin Trans. 1 1991, 361 - 363 G. Bellucci, C. Chiappe, L. Conti, F. Marioni, G. Pierini, Substrate Enantioselection in the Microsomal Epoxide Hydrolase Catalyzed Hydrolysis of Monosubstituted Oxiranes. Effects of Branching of Alkyl Chains ,./. Org. Chem. 1989, 54, 5978 - 5983. 

Water conjugation Water Epoxide hydrolase (microsomes) Arene oxides, cis-disubstituted and monosubstituted oxiranes Benzopyrene 7,8-epoxide, styrene 1,2-oxide, carbamazepine epoxide... 

Epoxide -> aliylic alcohol. Treatment of an oxirane with equimolar amounts of 1 and DBU in an aromatic solvent affords aliylic trimethylsilyl ethers in moderate yield. 2,2-Di-, tri-, and tetrasubstituted oxiranes, as well as oxides of cycloalkenes, react at 23° or below. 2,3-Di- and monosubstituted oxiranes do not react at this temperature these species react with 1 and DBU at 70-80° to give trimethylsilyl enol ethers. The reaction of epoxycyclooctane gives a product of transannular cyclization. In the case of epoxycyclohexane, the intermediate 2 has been isolated. 

Vinyllithium reageants, generated using Schlosser s reagent, attack monosubstituted oxiranes to produce homo-allylic alcohols (Equation 27) <1996T1433>. The addition reaction of lithiated alkynes to epoxides was observed to... 

Epoxides bonded to a chain of carbon atoms can also be named as derivatives of oxirane, the simplest epoxide having two carbons and one oxygen atom in a ring. The oxirane ring is numbered to put the O atom at position one, and the first substituent at position two. No number is used for a substituent in a monosubstituted oxirane. 

Few publications deal with the oxidation of the oxiranes. This method is used for synthetic purposes if it is difficult to prepare the desired compound by other means. Alkaline hydrogen peroxide induces splitting of a C-C bond in most terminal oxiranes. The result of the reaction is a disubstituted ketone via a 3-hydroperoxyalcohol (Eq. 153) monosubstituted oxiranes yield glycols. 

The effect of a heteroatom 0 to the oxirane ring has been studied in the reaction of monosubstituted oxiranes 131 and benzylamine. If X = 0, the reaction occurs via the transition state 132 with neighbouring-group participation. Neighboring-group participation has similarly been observed in the reactions of mono- and tri-substituted oxiranes and )3-substituted primary amines. The product ratio of the aminoalcohols formed from the reactions of a-vinyloxiranes and primary amines depends on the geometry of the oxirane.Base-catalyzed addition of oxiranes to oximes leads not only to 0-alkyl but to A -alkyl derivatives (Eq, 319). ... 

Base-promoted isomerizations of oxiranes by way of oxirane C—H abstraction are less common. Lithium tetramethylpiperidide (LiTMP) has successfully been used for this purpose <94CC2103>. Monosubstituted oxiranes are isomerized with LiTMP to aldehydes. 

When these results are compared with those from the polymerization of the other monosubstituted oxiranes (9), it should be emphasized that the partly crystalline fraction of poly(styrene oxide), I, obtained in the presence of the ZnEt2/H20 catalyst is so far the only polyoxirane reported which does not follow Bernoullian statistics. Only one other case, namely that of the polymerization of phenylthiirane by a coordination catalyst system, is known until now which follows first-order Markov statistics (10). 

These results for styrene oxide polymerization indicate clearly that when a monosubstituted oxirane is polymerized, one can expect the occurrence of various active centers and of different polymerization mechanisms in the reaction. 

Thus far, discussion has centered around the reaction of alkenes with a source of electrophilic oxygen as a route to epoxides [the C=C + O protocol]. However, a second general approach is represented by the reaction of carbonyl compounds with amphophilic carbon centers [the C=0 + C protocol]. For example, sulfonium yhdes are known to convert aldehydes and ketones to epoxides much recent work has focused on asymmetric induction using this methodology, a topic which has been the subject of a concise review in the past year <04ACR611>. As an illustration, the D-mannitol derived chiral sulfide 42 serves as a useful chiral auxiliary in the sulfonium methylide epoxidation of aldehydes to provide terminal monosubstituted oxiranes (e.g., 44) in fair to excellent yield and good enantiomeric excess <04CC1076>. 

Table 2.7 shows the free energies of polymerization of monosubstituted oxiranes. There are two conclusions coming from this Table. No direct correlation exists with... 

High yields of monosubstituted oxirans 90 ) have been obtained by the... 

Monosubstituted oxiranes ring open on interaction with the dianion of 4-(phenylsulfonyl)-butanoic acid and then cyclize by the addition of trifluoroacetic anhydride to give oxepan-2-ones, as cw-/t7flnj-mixtures <92SC239>. 

Red yeasts (e.g., Rhodotorula or Rhodosporidium sp.) give best enantioselectivities with monosubstituted oxiranes. 

George R BockCW, Glusker JP(1992) Protonation of monosubstituted oxiranes a computational molecular orbital study of oxonium ion versus carbonium ion formation. J Phys Chem... 

Reactions with Oxiranes, Oxetanes, and Aziridines. Lewis acids, lanthanide salts, and titanium tetraisopropoxide or aluminum isopropoxide catalyze the reactions of cyanotri-methylsilane with oxiranes, oxetanes, and aziridines, yielding ring-opened products. The nature of the products and the regio-selectivity of the reaction are primarily dependent on the nature of the Lewis acid, the substitution pattern in the substrate, and the reaction conditions. Monosubstituted oxiranes undergo regiospe-cific cleavage to form 3-(trimethylsiloxy)nitriles when refluxed with a slight excess of cyanotrimethylsilane in the presence of a catalytic amount of potassium cyanide-18-crown-6 complex (eqs 8-10). The addition of cyanide occurs exclusively at the least-substituted carbon. 

Vandenberg, following a particularly penetrating line of research, used the polymerization of cis- and trans-2,3-epoxybutane to distinguish the polymerization mechanisms of oxirane coordination polymerization and then to generalize this basic mechanism to monosubstituted oxiranes (95). The mechanism... 

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