Monoepoxides synthesis

The Gabriel synthesis represents another indirect but highly valuable approach to amines. Trost has demonstrated a method for the asymmetric ring-opening of butadiene monoepoxide by use of one equivalent of phthalimide, 7t-allylpalladium chloride dimer, and the chiral bisphosphine 22 (Scheme 7.37). The dynamic kinetic asymmetric transformation proceeded through a putative achiral intermedi-... 

Selective epoxidation of one of the double bonds in dialkenes is of practical interest (Table XVI). Although monoepoxides predominate at low H2O2 concentrations, the diepoxides are also formed at higher concentrations. The diallyl epoxides of bisphenol A are major intermediates in the adhesives industry, and their synthesis in solid-catalyzed reactions in an eco-friendly manner remains a challenge. 

The successful application of this method was illustrated with a series of model dienes, and with the formal synthesis of leukotriene A4 methyl ester, a complex polyene monoepoxide, from the intermediate epoxyundecadienoate 17 prepared by selective epoxidation of trienyl ester 16 (equation 17). 

New total syntheses9 of azabicyclo[4.2.1]nonanone (10) have now been elaborated. The first synthesis started with 5-azidocyclo-oct-l-ene (7). Reduction and iV-methylation (via the urethane), followed by treatment of the secondary amine with hypobromous acid and with base, gave a mixture of 9-methyl-9-azabicyclo[4.2.1]nonan-2a-ol (8) and its 2/3-isomer (9), contaminated with some azabicyclo[3.3.1]nonane analogue cf. (18). The second synthesis starts with the monoepoxide from cyclo-octa-1,5-diene (11). Treatment with methylamine and... 

The exceptionally facile epoxidation of allylic alcohols by tert-butyl hydroperoxide in the presence of vanadium catalysts, discussed earlier, has been used466,467 for the synthesis of complex molecules. Thus, geraniol (X) and linalool (XI) are selectively epoxidized to the previously unknown monoepoxides with f-Bu02 H-V 0(acac)2 466 ... 

The third type is common to monoepoxides of cyclic 1,3-dienes In five- to eight-membered rings and results in rearrangement to /3,y-unsaturated ketones in 55-80% yield. This isomerization can be utilized as one step in a route to 4-hydroxy-2-cycloenones. An example is a synthesis of 4-hydroxy-2-cyclopentenone formulated in equation (III). 

Mixed cyanocuprates, [RCuCN]Li. These cuprates (1) are prepared by addition of 1 equiv. of copper(I) cyanide to an alkyllithium in ether at -40°. [CH,CuCN]Li and [CeHsCuCNjLi add stereo- and regiospecifically to 1,3-cyclohexadiene monoepoxide (2) to give 3, which can be epoxidized by m-chloroperbenzoic acid to give 4 in high yield. The products (4) are valuable for stereocontrolled synthesis of trisubstituted cyclohexenols (scheme I). ... 

Selective introduction of an epoxide function was achieved during the total synthesis of racemic periplanone B. Dienone 30 [EEO = OCH(OEt)CH3] yielded monoepoxide 31 as the sole product when epoxidized with zm-butyl hydroperoxide/Triton B/tetrahydrofuran, while compound 32 gave a 4 1 mixture of diastereomers 33 and 34 87. Epoxidation of 35 gave single epoxide 3688, as well as the racemic version of the transformation 17— -18 (p 4667)89. 

During studies on the synthesis of aranorosin, model racemic cyclohexadienone 39 was epox-idized with dimethyldioxirane. After 14 days, isomeric monoepoxides 40 and 41 were isolated in 77% yield and 43 57 ratio. Prolongated treatment with dimethyldioxirane (35 days) gave additionally two bisepoxides 42 and 43. The ratio (40/41/42/43) was 32 48 8 1291. 

Trost has reported enhanced enantioselectivity in the desymmetrization of mero-biscarbamates in the presence of triethylamine. Under these conditions, high yields (>80%) and enantiomeric excesses (93-99% ee) are obtained. This methodology has been applied to the synthesis of (—)-swainsonine. a-Amino esters have been used as nucleophiles in the reaction with acyclic allylic esters and isoprene monoepoxide, providing access to diastereoselective N-alkylated a-amino esters. By employing the feature ligand, asymmetric palladium(0)-catalyzed cychzation of 2-(tosylamino)phenol with ( -l,4-bis[(methoxycarbonyl)oxy]but-2-ene provides 2-vinylbenzomorpholine in 79% ee. A number of alternative diphosphine ligands were studied and found to be inferior. 

Based on the structural diversity of the many congeners originating from Laurencia, the elucidation of a bios5mthetic mechanism for the likely development of these metabolites is of much interest. The isolation and characterization of monoepoxide 30 (Scheme 1) from Laurencia okamurai [15] has allowed investigators to postulate that this compound (30) may be a common precursor for the biosynthesis of all other secondary metabolites derived from squalene [3]. Its absolute stereochemistry was verified via asymmetric synthesis utilizing a Sharpless asymmetric epoxidation [16] of trans, trara-famesol,... 

Reactions of cycloalkadiene monoepoxides have received considerable attention. In general, cyanocu-prates have provided better Sn2 selectivity than lithium homocuprates, and the alternative Sn2 reaction is more competitive with vinyl- or phenyl-cuprates than with alkylcuprate reagents. Reactions of cy-clopentadiene monoepoxides with cyanocuprates have found application in prostaglandin synthesis. Effective electrophilic a -alkylation of cyclic enones can be accomplished by Sn2 cuprate addition to the corresponding epoxy enolate, enol phosphate or silyl enol ether. ... 

Transannular cyclizations of cyclodecadiene monoepoxides have been studied in exhaustive detail, particularly amongst natural germacranolides, because of their relevance to biogenetic models for the synthesis of eudesmane- and guaiane-type sesquiterpenes. " A full discussion of this topic is beyond the scope of this chapter, but the examples collected in equations (54-64) provide the reader with an in-... 

The research of Warrener et al. in this area has yielded a number of interesting oxabicyclopentane derivatives. In their epoxidation of the Cookson ester (30) a mixture of the two monoepoxides (31) and (32) was isolated (Equation (1)) <94TL1075>. Epoxidation of Nenitzescu s ester (33) with MCPBA, contrary to an earlier report <83JOU1390, 83ZOR1543), delivers a mixture of the three epoxides (34), (35), and (36) (Equation (2)). Several research groups have directed interest toward the synthesis of Dewar furan (5-oxabicyclo[2.1,0]pent-2-ene) and its derivatives these have been... 

Addition of low-molecular monoepoxides at the beginning and at the end of PETP synthesis allows to increase PETP hydrolysis resistance, thereby to improve physico-chemical properties of the fibre, to obtain polyester fibre with high degree of polymerization, to increase greatly thermal stability of polyester fibres. 

The microbial transformation of humulene, a substrate showing a structure similar to that of germacrone, was studied by Abraham and Stumpf using a screen of about 300 strains1175 . This led the authors to select the fungi Diplodia gossypina and Chaetonium cochlioides for preparative scale experiments. It was thus observed that the main reaction path starts with the epoxidation of the 1,2-double bond, as shown by direct biotransformation of this monoepoxide obtained by chemical synthesis. This is then further oxidized to yield a multitude of products including diepoxides and hydroxy-epoxides (Fig. 16.1-28). 

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