Michel Maffei

Phosphane–boranes: synthesis, characterization and synthetic applications

Abstract The chemistry of borane (BH 3 ) complexes of tricoordinated phosphorus compounds is reviewed, including the preparation, coordination chemistry, reactivity and synthetic applications.

Enantioselective reduction of ketones with borane, catalyzed by (S)-(−)-proline or (S)-(+)-prolinol.

Abstract The enantioselective reduction of ketones by borane in the presence of catalytic amounts of ( S )-(−)-proline or ( S )-(+)-prolinol as chiral auxiliaries has been investigated. The alcohols possess all the ( R ) configuration, and are obtained in good enantiomeric excess. A mechanistic rationale is proposed, involving an oxazaborolidine formed from ( S )-(+)-prolinol and borane.

The use of (4r,5r)-dicarboalkoxy 2-chloro 1,3,2-dioxaphospholanes as new chiral derivatizing agents for the determination of enantiomeric purity of alcohols by 31P NMR.

Abstract The title compounds are prepared from a dialkyl tartrate and PCl 3 . Their use as chiral derivatizing agents for the determination of enantiomeric excess of primary, secondary and tertiary alcohols by 31 P NMR is described.

PD(0) CATALYZED ASYMMETRIC AMINATION OF A PROCHIRAL BICYCLIC ALLYLIC DIACETATE

2,3-bis(acetoxymethyl)bicyclo[2.2.1]hepta-2,5-diene 1 undergoes nucleophilic attack of secondary amines under catalyzed Pd(0) reaction conditions. The influence of various tertiary amines as acceptor bases on the reaction as well as the nature of the organophosphorus ligands on the metal has been investigated. The use of chiral heterocyclic ligands led to the formation of the monoaminated product 2e with enantiomeric excess up to 89%.

Enantioselective synthesis of cyclic dialkyl (3-hydroxy-1-alkenyl) phosphonates by baker's yeast-mediated reduction of the corresponding enones

Abstract Cyclic dialkyl (3-oxo-1-cycloalkenyl) phosphonates were subjected to bakers yeast-mediated enantioselective reductions to afford the corresponding dialkyl (3-hydroxy-1-alkenyl) phosphonates. The six- and seven-membered ring enones were reduced with moderate to good enantiomeric excesses, whereas the five-membered ring substrate always yielded the double bond reduced compound. The use of different reduction conditions did not improve the ees markedly, but it was found, for the six-membered analogues, that the alkyl groups held by phosphorus influence dramatically the enantioselectivity of the reduction, leading to up to 95% enantiomeric excess.

Palladium catalysed allylic acetoxylation of dialkyl allyl phosphonates.

Abstract The catalytic acetoxylation of dialkyl allyl phosphonates with the Pd(OAc)2/benzoquinone/MnO2/HOAc system leads, regioselectively, to dialkyl 3- acetoxy 1-alkenyl phosphonates. On the basis of the regio- and stereoselectivity of the reaction, a mechanism is proposed which involves a (π-allyl) palladium complex as intermediate.

Enzymatic resolution of diethyl (3-hydroxy-1-butenyl) phosphonate

The enzymatic esterification of diethyl (3-hydroxy-1-butenyl) phosphonate 1 with different enzymes has been carried out, and allows the preparation of (S)-1 and (R)-diethyl (3-acetoxy-1-butenyl) phosphonate 2 with very high enantiomeric excess. The absolute conguration of 1 was determined by independent synthesis from (S)-ethyl lactate.

First enzymatic resolution of a phosphane–borane complex

The borane adduct of (2-hydroxypropyl)diphenylphosphane 1 was resolved by enantioselective esterification with CAL-B. (S)-1 was thus obtained with 91% enantiomeric excess. Its absolute configuration was determined by chemical correlation from (S)-propylene oxide.

Palladium-Catalyzed Acetoxylation of Cyclic Allyl Phosphonates in the Presence of Isopentyl Nitrite and Using Molecular Oxygen as Final Oxidant

Abstract The palladium-catalyzed acetoxylation of cyclic dialkyl allyl phosphonates is effected using palladium chloride as catalyst, in the presence of isopentyl nitrite in acetic acid under an oxygen atmosphere. The proposed mechanism for the reaction involves a palladium nitro–nitroso redox couple.

Evidence of Formation of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Carbon Nucleophiles

The palladium(0)-catalyzed alkylation of 2,3-bis(acetoxymethyl)bicyclo[2.2.1]hepta-2,5-diene 1 with malonate-type enolates as nucleophiles is investigated. A monoalkylated product is formed first, and undergoes (depending on the nucleophile used) a second intramolecular reaction leading to spirocyclopropane-annulated bicyclo[2.2.1]heptene derivatives 5. The formation of endo spirobicyclic cyclopropanes adducts as major isomer is rationalized by assuming formation of an intermediate exo-(π-allyl)palladium complex.