Alcohols stereoselective epoxidation

Similarly, diethylaluminum azide gives (3-azido alcohols. The epoxide of 1-methylcyclohexene gives the tertiary azide, indicating that the regiochemistry is controlled by bond cleavage, but with diaxial stereoselectivity. 

Asymmetric epoxidation of ailylic alcohols.1 Epoxidation of allylic alcohols with r-bulyl hydroperoxide in the presence of titanium(lV) isopropoxide as the metal catalyst and either diethyl D- or diethyl L-tartrate as the chiral ligand proceeds in > 90% stereoselectivity, which is independent of the substitution pattern of the allylic alcohol but dependent on the chirality of the tartrate. Suggested standard conditions are 2 equivalents of anhydrous r-butyl hydroperoxide with 1 equivalent each of the alcohol, the tartrate, and the titanium catalyst. Lesser amounts of the last two components can be used for epoxidation of reactive allylic alcohols, but it is important to use equivalent amounts of these two components. Chemical yields are in the range of 70-85%. 

Stereoselective epoxidation of an allylic alcohol (5. 75-76 9, 81-82). The antibiotic methyl pscudomonatc A (2) is the -epoxide of methyl pseudomonate C. Epoxidation of methyl pseudomonate C with m-chloropcrbenzoic acid in CH.Cl. 

Allylic and cis-homoallylic alcohols are epoxidized readily, but frans-homoallylic and bishomoallylic alcohols react slowly, if at all. The stereoselectivity in the epoxidation of acyclic allylic alcohols is the same as and is comparable to that observed with r-BuOOH/VO(acac)2. The stereoselectivity in epoxidation of acyclic homoallylic alcohols is also the same but lower than that obtained with t-BuOOH/ VO(acac)2. Epoxidation of cyclic allylic alcohols proceeds more slowly and in lower yield than that of acyclic allylic alcohols. 

NR = nonreactive toward hydrocarbons PO = oxidation of phosphines to phosphine oxides MF — peroxometallacyclic adduct formation with cyanoalkenes NSE — nonstereoselective epoxidation SE=stereoselective epoxidation AE = asymmetric epoxidation HA- hydroxylation of alkanes HB=hydroxylation of arenes OA = oxidation of alcohols to carbonyl compounds K = ketonization of Lermina 1 alkenes SO oxidation of S02 to coordinated S04 MO = metallaozonide formation with carbonyl compounds I = oxidation of isocyanides to isocyanates. 

Stereoselective epoxidation of /i-cw-homoallylic alcohols by vanadium, tungsten and molybdenum oxo species has been used for the construction of intermediates with four adjacent asymmetric centres346. 

Stereoselective epoxidation. A detailed study of epoxidation of homoallylic alcohols with this system indicates that the direction and degree of stereoselectivity can be predicted from a vanadate ester transition state with the chair comformation A. for example, the selectivity is > 100 1 when R1 and R4 = H and R3 and R - alkyl, since 1,3-interactions are minimal. R1 can also be a methyl group, but the reaction is slowed. When R1 = isopropyl and R3 = methyl, severe 1,3-interactions in both chair forms result in low asymmetric induction (2 1 selectivity).2... 

Chiral A-amidino-l,2,3,4-tetrahydropyridines undergo a stereoselective epoxidation-nucleophilic opening sequence with either alcohols or organozinc reagents to give 2,3,6-trisubstituted piperidines where the relationship between the 2- and 3-positions is cis (Equation 15) <2005OL2747>. 

Epoxidations of the allylic alcohols (144)P (145), (146 equation 50) and (148 equation 51) are highly stereoselective. The transformation of (148) to (149) is an example of the use of silyloxyalkenes in the stereoselective synthesis of trans a,3-epoxy alcohols. The epoxidation of the ester (150), which has a hydroxy allylic to a /ran.r-disubstituted double bond, does not exhibit high stereoselectivity (equation 52) the epoxidation is regioselective, involving only the C(13)—C(14) double bond. 

Stereoselective epoxidation of allylic alcohols (5,76 7,62-63). The effect of an allylic hydroxyl group on the stereoselectivity of epoxidation of a double bond is reinforced by a neighboring ether group. Typical examples are shown in equations (I) and (II). ... 

Takai, Oshima, and Nozaki achieved stereoselective epoxidation of allylic alcohols with Al(OBu )3-f-BuOOH (Sch. 16) ( )-allylic alcohols were converted predominantly into threo epoxy alcohols these are unfavorable products in epoxidations with VO(acac)2-f-BuOOH [36]. 

Epoxidation of acyclic allyl alcohols with peracid and Mo/TBHP displays an opposite stereospecificity to that for the V/TBHP system. Trimethylsilyl-substituted allylic alcohols give t/zreo-epoxyalcohols with MCPBA and erythro-alcohols with VO(acac)a-TBHP, with high stereoselectivity. In the stereospecific epoxidation of cis- and trans-allyl alcohols, formation of a transition state is assumed with the development of two H bonds between the hydrogen atom of the hydroxy group of the allyl alcohol and the oxygen of the peracid, and between the hydrogen of the peracid OH and the oxygen of the ether 10. An analysis of the diastereometric transition-state interactions for stereoselective epoxidation of acyclic allylic alcohols has been published. A conformational effect may be responsible for the unexpected cis major product in Eq. 2. 

The kinetic and stereochemical results on 2-methylenecyclohexanol derivatives have been utilized to interpret the stereoselective epoxidation of aliphatic a-ethylene-alcohols. The main product in the oxidation of 4-a-chloro-3(10)-carene 16 is 17 (Eq. 7). ... 

By equatorial attack on the carbonyl, a single stereoisomer is formed from tert-butylcyclohexanone. In the presence of sodium alcoholate, 84 is formed from a butadienyl-sulfonium salt with an aldehydeThe reaction is stereospecific with 85 for instance, with aldehydes the trans product is obtained.An interesting stereospecific intramolecular methylene transfer has been observed for a decalone derivative. Stereoselective epoxidation has recently been described with 79 predominantly, the trans product results. Epoxidation can be carried out in a one-pot procedure at room temperature, with MejS + Me2S04, then NaOMe formed in situ. ... 

Molybdenum hexacarbonyl, Mo(CO)6 [328], and molybdenum ace-tylacetonate, Mo02(acac)2 [530], catalyze the stereoselective epoxidation of allylic alcohols with tert-butyl hydroperoxide. 

NR s not reactive toward hydrocarbons S = stereoselective epoxidation E = epoxidation HA = hydroxylation of alkanes OA = oxidation of alcohols to carbonyl compounds PO oxidation of phosphines to phosphine oxides OC = oxidative cleavage of alkenes K= ketonization of alkenes DO = hydroxylation of alkenes to diols AO al1ylic oxidation of alkenes. 

---