André H.M. de Vries

Enantioselective Conjugate Addition of Diethylzinc to Chalcones Catalysed by Chiral Ni(II) Aminoalcohol Complexes

Abstract Conjugate addition of diethylzinc to chalcones is catalysed by complexes prepared in situ from Ni(acac) 2 and cis-exo-N,N -dialkyl-3-aminoisoborneols or (+)- cis-endo-N,N -dimethyl-3-aminoborneol ((+)-DAB) ( 13b ). The products are obtained with enantioselectivities up to 84 %. When scalemic (−)- cis-exo-N,N -dimethyl-3-aminoisoborneol ((−)-DAIB) ( 3c ) was employed in the reaction a positive nonlinear relationship was found. Several factors which govern catalyst activity and enantioselectivity have been investigated.

(+)-camphor-derived tri- and tetradentate amino alcohols; synthesis and application as ligands in the nickel catalyzed enantioselective conjugate addition of diethylzinc

Abstract Several novel tri- and tetradentate amino alcohol ligands, all derived from (+)-camphor, have been synthesized by using specific N -alkylation procedures. The amino alcohols were employed as chiral ligands in the nickel catalyzed conjugate additions of diethylzinc to chalcone and cyclohexenone as model substrates. For the acyclic enone enantioselectivities up to 83% were achieved.

Catalytic epoxidation of unfunctionalized alkenes by dinuclear nickel(II) complexes

The synthesis, crystal and molecular structure and catalytic activity in epoxidation reactions of new dinuclear nickel(II)-complexes, octahedral mu-diacetato-mu-[2,6-bis[N-2-(2-pyridylethyl) formimidoyl]phenolato]bisnickel(II). perchlorate . methanol (6) and square planar (mu-hydroxo-mu-[2,6-bis[N-((S)-1-benzyl-2-yl-pyrrolidine)formimidoyl]phenolato]bisnickel(II)-bisperchlorate (7), are described. For the preparation of 7 a new 5-step route for homochiral bisamine (S)-benzyl-2-aminomethyl-pyrrolidine (19) was developed starting from (S)-proline. Epoxidation of unfunctionalized alkenes with sodium hypochlorite and tert-butyl hydroperoxide as terminal oxidants was effectively catalyzed with bisnickel(II)-complexes 6 and 7, and a turnover of 165 was reached using trans-beta-methylstyrene (34). The epoxidations probably proceed via a radical intermediate (such as OCl .) and no enantioselectivity is obtained under phase transfer conditions. In epoxidation reactions employing tert-butyl hydroperoxide as terminal oxidant a turnover of 43 was obtained with trans-stilbene (30) as substrate. Unexpectedly in the case of styrene (29) 1,2-bis-(tert-butylperoxy)ethylbenzene (59) was isolated as the major product.

New bidentate chiral phosphoramidites in copper-catalyzed asymmetric 1,4-addition of diethylzinc to cyclic α,β-enones: enantioselective tandem 1,4-addition-aldol reactions with 2-cyclopentenone

New bidentate phosphoramidites were prepared starting from α,α,α,α-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) or 1,1-bi-2-naphthol (BINOL) and either 1,2-ethylene- or 1,3-propylenediamine N,N-disubstituted with achiral or chiral groups. The use of these ligands in the copper-catalyzed enantioselective conjugate addition of diethylzinc to 2-cyclohexenone and 2-cyclopentenone afforded products with e.e.s of up to 89 and 83%, respectively.

Diastereoselective synthesis of pyridyl substituted thiazolidin-4-ones. New ligands for the Cu(I) catalyzed asymmetric conjugate addition of diethylzinc to enones

Abstract Several novel thiazolidin-4-ones have been synthesized from chiral non-racemic α-mercapto acids by a three component reaction in high yields and with diastereomeric excesses up to 91%. After recrystallization, the thiazolidinones were obtained diastereomerically pure and were employed as chiral ligands in the copper catalyzed conjugate addition of diethylzinc to cyclohexenone and chalcone as model substrates. Enantioselectivities up to 62% were achieved.

Enantioselective conjugate addition of diethylzinc to chalcone catalyzed by Co(acac)(2) and chiral amino alcohols

Co(acac)2 in the presence of chiral ligands has been employed as catalyst for the enantioselective conjugate addition of diethylzinc to chalcone. With chiral amino alcohols derived from (+)-camphor, enantioselectivities up to 83% were achieved.