1.2- Diols oxirane synthesis

This classical example of oxirane synthesis involves treatment of a halohydrin with base <84CHEC-1(7)115,85CHE1,85MI103-01). Kolb and Sharpless introduced a three-step protocol <92X10515,92TL2095) whereby chiral diols, available by Sharpless asymmetric dihydroxylation <92JOC2768>, are efficiently converted into chiral oxiranes (Scheme 55). 

Alcohols with a nucleofuge leaving group in the r-position can be cyclized to give oxetanes. Thus the cyclodehydrohalogenation of halo alcohols occurs in an analogous way to the oxirane synthesis from y -halogenated alcohols (see p 20). Oxetanes can be prepared from 1,3-diols via monoarene sulfonates ... 

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

One of the first applications of the microbial hydrolysis of epoxides for the synthesis of a bioactive compound is based on the resolution of a 2,3-disub-stituted oxirane having a cis-configuration (Scheme 14). Thus, by using an enzyme preparation derived from Pseudomonas sp., the (91 ,10S)-enantiomer was hydrolyzed in a frans-specific fashion (i.e. via inversion of configuration at C-10) yielding the 9R,10R)-threo-diol. The remaining (9S,101 )-epoxide was converted into (-1-)-dispar lure, the sex pheromone of the gypsy moth in >95% ee [101]. 

Another illustration of the use of such a biocatalytic approach was the synthesis of either enantiomer of a-bisabolol, one of these stereoisomers (out of four) which is of industrial value for the cosmetic industry. This approach was based on the diastereoselective hydrolysis of a mixture of oxirane-diastereoiso-mers obtained from (R)- or (S)-limonene [68]. Thus,starting from (S)-hmonene, the biohydrolysis of the mixture of (4S,81 S)-epoxides led to unreacted (4S,8S)-epoxide and (4S,8i )-diol. The former showed a diastereomeric purity (> 95%) and was chemically transformed into (4S,8S)-a-bisabolol. The formed diol... 

A facile synthesis of 180 with a better yield has been developed as follows. O-Deacetylation of 51 with hydrochloric acid gave DL-(l,3/2)-3-bromomethyl-5-cyclo-hexene-1,2-diol (181). Stereospecific epoxidation of 181 with mCPBA and subsequent acetylation gave-the epoxide (182), which afforded the exocyclic methylene derivative (183) by dehydrobromination with silver fluoride [51]. Reductive cleavage of the oxirane ring of 183 with lithium aluminium hydride, followed by acetylation yielded... 

Allyl glycidyl ether is used the most since this monomer is commercially available. However, the synthesis requires a further step the chemical change of the oxirane into the diol. 

The synthesis of carbamic esters of 1,2-diols has been achieved by reacting oxiranes and amines in an atmosphere of carbon dioxide under various experimental conditions. ... 

There are various procedures for the preparation of polyethers. These procedures typically start with oxirane or oxirane derivatives (e.g. propylene oxide, etc.). Base catalyzed anionic polymerization, acid initiation, or complex coordination catalysis can be used for the reaction [1-3], Not only oxiranes can generate polyethers. Diols also can be used for polyether synthesis. Other source compounds include tetrahydrofuran, which can be polymerized to a polyether using fluorosulfonic acid (HSO3F) as a catalyst, oxetane (trimethylene oxide) or oxetane derivatives, which can be polymerized to generate polyethers with practical applications such as poly[bis(chloromethyl)oxetane], etc. 

Based on the deracemization of ( )-3-methyl-2-(4-pentenyl)-oxirane (Fig. 11.2-16) using Nocardia EH1 and sulfuric acid in dioxane containing a trace amount of water (see above), (S)-2-methyl-hept-6-ene-l,2-diol was obtained in 97% yield and 99% eet109I. This intermediate was successfully applied in a short synthesis of (S)-... 

---