Vinyl esters enol phosphates

Intermediate 37 can be transformed into ( )-thienamycin [( )-1)] through a sequence of reactions nearly identical to that presented in Scheme 3 (see 22— 1). Thus, exposure of /(-keto ester 37 to tosyl azide and triethylamine results in the facile formation of pure, crystalline diazo keto ester 4 in 65 % yield from 36 (see Scheme 5). Rhodium(n) acetate catalyzed decomposition of 4, followed by intramolecular insertion of the resultant carbene 3 into the proximal N-H bond, affords [3.2.0] bicyclic keto ester 2. Without purification, 2 is converted into enol phosphate 42 and thence into vinyl sulfide 23 (76% yield from 4).18 Finally, catalytic hydrogenation of 23 proceeds smoothly (90%) to afford ( )-thienamycin... 

Appropriate quenching of a reductively formed lithium enolate with a carboxylic acid anhydride, chloride, methyl chloroformate or diethyl phosphorochloridate yields the corresponding enol esters, enol carbonates or enol phosphates. These derivatives may be transformed into specific alkenes via reductive cleavage of the vinyl oxygen function, as illustrated by the example in Scheme 8. 

This methodology has also been applied to the conversion of alkyl esters into vinyl ethers with high stereoselectivity favoring the (Z)-isomer (Scheme 30). While standard Li/amine reduction conditions were not applicable, the enol phosphates could be reduced using triethylaluminum and tetrakis(tri-phenylphosphine)palladium. 

Tris(trimethylsilyl)phosphites, analogous to trialkylphosphites, undergo Perkow reaction with a-halo carbonyl compounds to give vinyl phosphates.223 Reaction of a-chloroketone 19 with trimethylphosphite produces dimethyl enol phosphate 20, which is further converted to b is [trimethyls ilyl] esters 21 using MeaSiBr. 21 is also produced directly from a-chloroketone 19 on reacting with P(SiMe3)3. 

Aldehydes, ketones and esters of general formula 708 reacted with amidines to give pyrimidine derivatives (Table 40, Entries 1-4). Analogous methods were developed for (per)fluorinated vinyl halides 709 (Entry 5) and 710 (Entries 6, 7). Analogous reaction was successful with enol phosphate 814, obtained from ketone 813 and sodium diethyl phosphite (Scheme 162) [120], In aU these cases, nucleophilic substitution of two fluorine atoms at a-carbon of the perfluoroalkyl group occurred. 

Phosphate groups can also be removed by dissolving-metal reduction. Reductive removal of vinyl phosphate groups is one method for conversion of a carbonyl compound to an alkene.224 (See Section 5.7.2 for other methods.) The required vinyl phosphate esters are obtained by phosphorylation of the enolate with diethyl phospho-rochloridate or /V A /V -tetramethyldiamidophosphorochloridate.225... 

Addition to linear 1,1-disubstituted allylic acetates is slower than addition to monosubstituted allylic esters. Additions to allylic trifluoroacetates or phosphates are faster than additions to allylic carbonates or acetates, and reactions of branched allylic esters are faster than additions to linear allylic esters. Aryl-, vinyl, alkynyl, and alkyl-substituted allylic esters readily undergo allylic substitution. Amines and stabilized enolates both react with these electrophiles in the presence of the catalyst generated from an iridium precursor and triphenylphosphite. 

Corey and Wright have utilized reductive conversion of a vinyl diethyl phosphate (73) to an alkene 74 in a synthesis of colneleic ester via the enol esters 72.43... 

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