Oxirane, 2,2-dimethyl-3-

Epoxyfarnesol was first prepared by van Tamelen, Stomi, Hessler, and Schwartz 4 using essentially this procedure. It is based on the findings of van Tamelen and Curphey5 that N-bromosuccinimide in a polar solvent was a considerably more selective oxidant than others they tried. This method has been applied to produce terminally epoxidized mono-, sesqui-, di-, and triterpene systems for biosynthetic studies and bioorganic synthesis.6 It has also been applied successfully in a simple synthesis of tritium-labeled squalene [2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-hexamethyl-, (all-E)-] and squalene-2,3-oxide [Oxirane, 2,2-dimethyl-3-(3,7,12,16,20-pentamethyl-3,7,ll,-15,19-heneicosapentaenyl)-, (all-E)-],7 and in the synthesis of Cecropia juvenile hormone.8... 

Oxiran 2,2-Dimethyl-3-(4-nitro-benzoyloxymethyl)- E21e, 4692 (En-Oxigenier.)... 

Vinyl oxirane 2-Methyl-2-vinyl oxirane 2-Methyl-2-(2-propenyl) oxirane 2,2-Dimethyl-3-(2,2-dimethylvinyl) oxirane... 

Dimethyl-(2-hydroxy-alkoxy)- (2,4,6-Trinitro-benzolsulfonate) Ell, 372 (R2SO + Oxiran) Dimethyl-(2-morpholino-l-alkenyl)-(Fluorsulfonate) Ell, 467... 

Dimethyl-(1,1 -dimethyl-2-hydroxy-ethoxy)- (2,4,6-trinitro-benzolsul-fonat) Ell, 371 (R2SO 4- Oxiran) Dimethyl-(2-hydroxy-butyloxy)-(2,4,6-trinitro-benzolsulfonat) Ell, 371 (R2SO 4-Oxiran) Dimethyl-(l-hydroxymethyl-propyl-oxy)- (2,4,6-trinitro-benzolsulfo-nat) Ell, 371 (R2SO 4- Oxiran)... 

Molecular orbital calculations predict that oxirane forms the cyclic conjugate acid (39), which is 30 kJ moF stabler than the open carbocation (40) and must surmount a barrier of 105kJmoF to isomerize to (40) (78MI50500). The proton affinity of oxirane was calculated (78JA1398) to be 807 kJ mol (cf. the experimental values of 773 kJ moF for oxirane and 777-823 kJ moF for dimethyl ether (80MI50503)). The basicity of cyclic ethers is discussed in (B-67MI50504). 

A dramatic decrease in the magnitude of the magnetic susceptibility anisotropy is observed on going from thiirane to the open-chain analog, dimethyl sulfide, and has been attributed to non-local or ring-current effects (70JCP(52)5291). The decrease also is observed to a somewhat lesser extent in oxirane relative to dimethyl ether. 

Alcoholic potassium hydroxide or sodium hydroxide are normally used to convert the halohydrins to oxiranes. Other bases have also been employed to effect ring closure in the presence of labile functional groups such as a-ketols, e.g., potassium acetate in ethanol, potassium acetate in acetone or potassium carbonate in methanol.However, weaker bases can lead to solvolytic side reactions. Ring closure under neutral conditions employing potassiunT fluoride in dimethyl sulfoxide, dimethylformamide or A-methyl-pyrrolidone has been reported in the patent literature. 

Due to the abundance of epoxides, they are ideal precursors for the preparation of P-amino alcohols. In one case, ring-opening of 2-methyl-oxirane (18) with methylamine resulted in l-methylamino-propan-2-ol (19), which was transformed to 1,2-dimethyl-aziridine (20) in 30-35% yield using the Wenker protocol. Interestingly, l-amino-3-buten-2-ol sulfate ester (23) was prepared from l-amino-3-buten-2-ol (22, a product of ammonia ring-opening of vinyl epoxide 21) and chlorosulfonic acid. Treatment of sulfate ester 23 with NaOH then led to aziridine 24. ... 

Dimethyl-oxiran wirddagegenunter ahnlichenBedingungen in 55%iger Ausbeute zu einem Alkohol-Gemisch reduziert, das 5—7% tert.-Butanol und 93—95% 2-Methyl-propanol enthalt7 ... 

Die Stereochemie der Oxiran-Reduktionen mit Lithiumalanat entspricht dem SN2-Mechanismus. Chirale Oxirane werden unter Walden-Umkehr aufgespalten. So erhalt man z.B. aus r>(+)-2,3-Dimethyl-oxiran mit Lithium-tetradeuterido-aluminat in 86% iger Ausbeute r>(-)-erythro-3-Deutero-butanol-(2)i2. 

Dimethyl-1,2-benzenediamine (384) and 2,2,3-trifluoro-3-trifluoromethyl-oxirane (385) gave 3-trifluoromethyl-2(l//)-quinoxalmone (386) (NaHCOs, CH2Cl2-Et20, 23°C, sealed, 12 h 78%) analogs similarly. 

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

In selective etherification, it is important to distinguish between reversible and irreversible reactions. The former class comprises etherifications with dimethyl sulfate, halogen compounds, oxirane (ethylene oxide), and diazoalkanes, whereas the latter class involves addition reactions of the Michael type of hydroxyl groups to activated alkenes. In this Section, irreversible and reversible reactions are described separately, and a further distinction is made in the former group by placing the rather specialized, diazoalkane-based alkylations in a separate subsection. 

Let us take the example of 2-butene to make the point clear. Since it exists in cis and trans forms, it reacts with peroxy acids in a stereospecific way. The cis form gives only cis-2, 3 dimethyl oxirane while the trans. form gives only trans-2, 3 dimethyl oxiranes. 

Figure 4. Symmetry breaking of the ethanol torsion potential (top, two gauche and one trans conformation) by interaction with a chiral acceptor molecule (dimethyl oxirane, bottom), in this case RR trans 2,3 dimethyloxirane [128]. Note that trans ethanol is less stable in the complex and that the two gauche (g) forms differ in energy.

Scheme 2.7 Influence of dimethyl sulfide on the Sn2 substitution of propargyl oxirane 20.

The beneficial effect of added phosphine on the chemo- and stereoselectivity of the Sn2 substitution of propargyl oxiranes is demonstrated in the reaction of substrate 27 with lithium dimethylcyanocuprate in diethyl ether (Scheme 2.9). In the absence of the phosphine ligand, reduction of the substrate prevailed and attempts to shift the product ratio in favor of 29 by addition of methyl iodide (which should alkylate the presumable intermediate 24 [8k]) had almost no effect. In contrast, the desired substitution product 29 was formed with good chemo- and anti-stereoselectivity when tri-n-butylphosphine was present in the reaction mixture [25, 31]. Interestingly, this effect is strongly solvent dependent, since a complex product mixture was formed when THF was used instead of diethyl ether. With sulfur-containing copper sources such as copper bromide-dimethyl sulfide complex or copper 2-thiophenecarboxylate, however, addition of the phosphine caused the opposite effect, i.e. exclusive formation of the reduced allene 28. Hence the course and outcome of the SN2 substitution show a rather complex dependence on the reaction partners and conditions, which needs to be further elucidated. 

Method B (polymer-supported) The aldehyde or ketone (1.4 mmol) is added to S,S-dimethyl polystyrylsulphonium fluorosulphonate (2 g) suspended in CH2CI2 (15 ml) and the mixture is stirred with aqueous NaOH (65%, 2 ml) and TBA-I or TBA-OH (0.6 mmol) until the carbonyl compound has been consumed. The filtered solution is extracted with H,0 (3 x 25 ml) and evaporated to yield the oxirane (e.g. from PhCHO,... 

Asymmetric induction using catalytic amounts of quininium or A-methyl-ephedrinium salts for the Darzen s reaction of aldehydes and ketones with phenacyl halides and chloromethylsulphones produces oxiranes of low optical purity [3, 24, 25]. The chiral catalyst appears to have little more effect than non-chiral catalysts (Section 12.1). Similarly, the catalysed reaction of sodium cyanide with a-bromo-ketones produces epoxynitriles of only low optical purity [3]. The claimed 67% ee for the phenyloxirane derived from the reaction of benzaldehyde with trimethylsul-phonium iodide under basic conditions [26] in the presence of A,A-dimethyle-phedrinium chloride was later retracted [27] the product was contaminated with the 2-methyl-3-phenyloxirane from the degradation of the catalyst. 

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