Phosphines, alkylation epoxides

Natural Products.—A number of one-step olefin syntheses have appeared in which phosphine, alkyl halide, and carbonyl compound are allowed to react together in the presence of a suitable epoxide as the source of base. Among them are the synthesis of ( )-mitorubrin and of the polyene (97) (Scheme 5). ... 

Nguyen and co-workers have developed a method for the alkylation of meso-epoxides by a preformed NHC AIEtj complex (Eq. 29) [117, 154], This method is a natural extension of previous work utilizing triethylaluminum and catalytic phosphines for ring opening of epoxides [155],... 

All the polymers of Table III have been applied for the epoxidation of olefins with alkyl hydroperoxides. For example, the polymers with iminodiacetic acid or diethylene triamine groups were used for the regioselective epoxidation of (E)-geraniol with t-BuOOH to the 2,3-epoxide (225), whereas the Mo anchored to the diphenylphosphinopolystyrene catalyst is used in the epoxidation of cyclohexene with t-BuOOH (228). The polymer-supported molybdenyl thioglycolate has also been used for the catalytic oxidation of thiols and phosphines with air or pyridine N-oxide as the oxidant (234). 

In the reaction of butyllithium or lithium di-isopropylaminc with the Mannich bases derived from hydrogen cyanide, phosphine oxides, and phosphorous esters, as well as from phenols, jhc metal atom is prevalently bound to the CH2—N moiety (313 in big. 119, route b). This intermediate is then allowed to react with halides, epoxides, and other alkylating reagents in order to link an alkyl group to methylene. Under proper conditions, aldehydes, ketones and enamines can be prepared by this method. 

Although Smh is more chemoselective than traditional dissolving metal reagents, it does react with sulfoxides, epoxides, the conjugated double bonds of unsaturated ketones, aldehydes and esters, alkyl bromides, iodides and p-toluenesulfonates. It does not, however, reduce carboxylic acids, esters, phosphine oxides or alkyl chlorides. In common with most dissolving metal systems, ketones with an a-hetero substituent suffer loss of the substituent rather than reduction of the carbonyl group. ... 

Warren and coworkers have described the alkylation of (diphenylphosphinoyl)alkyllithiums with epoxides as an effective means of synthesizing 3-(diphenylphosphinoyl) ketones, homoenolate anion equivalents. The treatment of the adducts of lithiated phosphine oxides and epoxides with base to form cyclopropanes was reported by Toscano et al ... 

Peroxides and Related Compounds.— Triphenylphosphine has been shown to react with the dioxetan (61) to give the quinquecovalent compound (62). This decomposes to give an epoxide on heating. Several peroxides and polyperoxides react with alkyl- and aryl-phosphines in the presence of water. Alcohols are... 

Method E is similar to method D in that it relies upon the nucleophilic cleavage of epoxides to generate stereochemically defined betaines. A two-step procedure is employed, starting with the reaction of a lithium phosphide with the cis or trans epoxides (36 or 37). The resulting alkoxy phosphines 34 or 35 are converted into betaines by direct alkylation with methyl iodide (19). This contrasts with method A where the betaine is generated by the deprotonation of a -hydroxyphosphonium salt, and method E may therefore produce a different population of betaine rotamers than does method A. This subtle difference may explain why method E proceeds with higher stereospecificity than does method A in the Trippett-Jones experiment (Table 7 entry 16,... 

Application of the Abramov reaction has received little more attention, but it has been used in conjunction with toluenesulphonyl derivatives of hydroxyketones in the presence of dbu (Scheme 28) when acted upon by thiourea in MeOH at room temperature, the oxi-ranes 344 (R = Me or Et, R = Me or Cy) are converted into the corresponding thiiranes 345 ". The reaction between the protected oxoacetal 346 with methyl phenylphosphinate in the presence of dbu provides the epoxide 347 as a mixture of the diastereoisomeric 4RS and 4SR pairs in the ratio 7 3. Reduction of the product with H2 and Raney nickel yields the linear phosphinate ester 348 Similarly, the reactions between the ketose 349 (R = Me or CH2Ph) with either dialkyl hydrogenphosphonate or alkyl phenylphosphinate, again in the presence of dbu, gave the epoxides 350 (R = Me or CH2Ph R = R = MeO R = Ph,... 

Cyclic /neso-epoxides, such as cyclopentene oxide (64), can be induced to undergo alkylative ring-opening in the presence of trialkylaluminum reagents under catalysis using N-heterocyclic carbenes (62). These unusual catalysts are derived from the deprotonation of imidazolinium salts (61), and serve as phosphine mimics in terms of electron-pair donation behavior to form aluminum complexes of the type 63 <01 OL2229>. 

---