Peter Warner

Chiral propionate enolate equivalents for the stereoselective synthesis of threo- or erytho-α,-methyl-β-hydroxy acids

Abstract The aluminium and copper enolates derived from (η5-C5H5)Fe(CO)(PPh3)COCH2CH3 are chiral propionate enolate equivalents which on reaction with aldehydes (RCHO, RMe.Et,iPr,tBu) provide stereoselective syntheses of threo- and erytho-α-methyl-β-hydroxy acids respectively.

Chiral acetate enolate equivalent for the synthesis of β-hydroxy acids and esters: X-ray crystal structure of RR,SS-[(η5-C5H5)Fe(CO)(PPh3)(COCH2CH(OH)CH2CH3)]

Abstract The aluminium enolate derived from the iron acetyl complex [(η5-C5H5Fe(CO)(PPh3)COCH3], in contrast to the lithium enolate, undergoes highly stereoselective aldol reactions with aldehydes to generate RR,SS-β-hydroxyacyl complexes which on decomplexation liberate β-hydroxy acids or esters. Determination of the molecular structure of RR,SS-[η5-C5H5)Fe(CO)(PPh3)(COCH2CH(OH)CH2CH3] allowed assignment of the relative configuration of the new chiral centre.

Improved stereochemical control and mechanistic aspects of the alkylation of enolates derived from [(η5-C5H5)Fe(CO)(PPh3)COCH2R]

Abstract An analysis of the factors controlling the stereoselective alkylation reations of enolates derived from [(n 5 -C 5 H 5 )Fe(CO)(PPh 3 )COCH 2 R] results in an amelioration in the observed stereoselectivities to >200:1.

Stereoselective synthesis of erythro-β-hydroxy carboxylic acids via iron acyl complexes

Abstract β-Hydroxy acyl ligands bound to (η 5 -C 5 H 5 )Fe(CO)(PPh 3 ) are stereoselectively alkylated on the α-carbon to give after decomplexation erythro -β-hydroxy carboxylic acids.

Synthesis and Characterisation of E and Z α,β-Unsaturated Acyl Complexes [(η5-C5H5)Fe(CO)(PPh3)(COCH=CHR)] (R=H, Me, Et, n-Bu, t-Bu, Ph, vinyl,2-furyl)

Abstract α,β-Unsaturated acyl complexes of the chiral auxiliary [(η5-C 5 H 5 )Fe(CO)(PPh 3 )] can be generated in high yield as readily separable mixtures of E and Z isomers by the Peterson olefination reaction between [(η 5 -C 5 H 5 )Fe(CO)(PPh 3 )COCH 2 SiMe 3 ] and aldehydes RCHO (R=H, Me, Et, n -Bu, t -Bu, Ph, vinyl, 2-furyl). The Wittig reaction between [(η 5 -C 5 H 5 )Fe(CO)(PPh 3 )COCH=PMe 3 ] and benzaldehyde stereoselectively generates E-[(η5-C 5 H 5 )Fe(CO)(PPh 3 )COCH=CHPh]. α-Trimethyl-silylation of both diastereoisomers of the β-hydroxy complexes [(η 5 -C 5 H 5 )Fe(CO)(PPh 3 )COCH 2 CH(OH)R] gives completely stereoselectively the corresponding E α,β-unsaturated acyl complexes [(η 5 -C 5 H 5 )Fe-(CO) (PPh 3 )COCH=CHR], These E α,β-unsaturated acyl complexes are also formed stereoselectively, in high yield via sodium hydride induced elimination of methanol from the β-methoxy complexes [(η 5 -C 5 H 5 )Fe(CO)(PPh 3 )COCH 2 CH(OMe)R] (R=H, Me, Et, n -Bu, Ph, vinyl, 2-furyl).

Chiral discrimination in the reactions of the enolate E-[(η5-C5H5)Fe(CO)(PPh3)COCHMe]−Li+ with cis and trans but-2-ene oxides in the presence of BF3·OEt3

cis and trans-but-2-ene oxides undergo SN2 opening with the lithium enolate derived from [(η5-C5H5)Fe(CO)(PPh3)COCH2CH3] in the presence of BF3·OEt2; preferential opening occurs where the enolate configuration at iron matches that of the epoxide carbon being attacked.

Disubstituted vinylidene complexes of iron and ruthenium: nucleophilic properties of ν1-acetylide ligands

Abstract The η1-acetylide complexes (C5H5)ML2(CCR) (M  Fe, Ru; L  PPh3, L2  Ph2PCH2CH2PPh2) are nucleophilic at the β-carbon and react with a variety of mild electrophiles to yield the corresponding disubstituted vinylidene complexes [(C5H5)ML2 (CCR′) PF6.

Chiral acetate enolate equivalent for the synthesis of β-hydroxy acids

The aluminium enolate derived from (η5-C5H5)Fe(CO)(PPh3)(COMe) undergoes stereoselective aldol condensations with aldehydes to generate β-hydroxy acyl complexes which yield β-hydroxy acids on decomplexation.

Base promoted rearrangements of cyclopentadienylacyl- and -carboxyalkyl-metal complexes

Treatment of the complexes [(η5-C5H5)Fe(CO)(PPh3)COCH2R] and [(η5-C5H5)Fe(CO)(PPh3)CO2R] with n-butyllithium followed by methyl iodide gives the rearranged products [(η5-C5H4COCH2R)Fe(CO)(PPh3)Me] and [(η5-C5H4CO2R)Fe(CO)(PPh3)Me] respectively; the former reactions are stereospecific.

Stereoselective template-directed C-glycosidation. Synthesis of 5-membered oxygen heterocycles via cation-mediated intramolecular cyclization reactions

Construction of 5-membered oxygen heterocycles by intramolecular template-directed C-glycosidation is described. Alkylation of thioglycoside 5 with enone 6 followed by enol etherification gave cyclization substrates 8. Compound 8a underwent silver(I) trifluoromethanesulfonate-mediated ring-closure to give a 1.7:1 mixture of 9α and 9β; isomer 8s gave an 8.5:1 ratio. Some derivatization reactions of the bicyclic products are described.