Dario Pini

Heterogeneous asymmetric epoxidation of unfunctionalized olefins catalyzed by polymer-bound (salen)manganese complexes

Abstract The synthesis of three different polymer-bound chiral Mn-salen complexes (Poly- 1, -2a, -2b ) is reported, along with their application as recyclable catalysts in heterogeneous asymmetric epoxidation with m CPBA/NMO of several unfunctionalized olefins. The introduction of a spacing group between the polymeric chain and the metal centre (Poly- 2a and -2b ) considerably increased the enantioselectivity of the process.

Polymer-bound chiral (salen)Mn(III) complex as heterogeneous catalyst in rapid and clean enantioselective epoxidation of unfunctionalised olefins

The application of a new polystyrene-divinylbenzene system containing an optically active (salen)Mn(III) complex in asymmetric epoxidation of unfunctionalised olefins is reported. This system showed a remarkably high reaction speed in the conditions described. Reaction outcomes drastically varied, in terms of enantioselectivity and cis-trans isomerization extent, upon the terminal oxidant employed (mCPBANMO and MMPP). Reuse of the catalyst was extremely efficient for several cycles. Interesting values of ee were obtained for styrene (15%) and cis-β-methylstyrene (41%).

FIRST EXAMPLE OF A SILICA GEL-SUPPORTED OPTICALLY ACTIVE MN(III)-SALEN COMPLEX AS A HETEROGENEOUS ASYMMETRIC CATALYST IN THE EPOXIDATION OF OLEFINS

Abstract An optically active Mn(III)–salen complex was supported on silica gel materials: the insoluble systems obtained were employed as catalysts in the asymmetric epoxidation of some aromatic olefins. Enantiomeric excess values up to 58% were obtained.

Cinchona alkaloids for preparing new, easily accessible chiral stationary phases.I. 11-(10,11-Dihydro-6′-methoxy-cinchonan-9-OL)-tiopropylsilanized silica.

Abstract By reaction of mercatopropylsilanized silica with quinine in the presence of AIBN as radical initiator, a silica supported alkaloid can be obtained, which is effective in the HPLC resolution of racemic arylalkylcarbinols and binaphtol derivatives.

Cinchona alkaloids for preparing new, easily accessible chiral stationary phases : II. Resolution of binaphthol derivatives on silica-supported quinine☆

Abstract The preparation of the new chiral stationary phase SiSQuin, obtained by reaction of γ-mercaptopropylsilanized silica with the commercially available Cinchona alkaloid quinine, is described. This support is efficient for the rapid (6–7 min) separation of some binaphthol derivatives (separation factors between 1.08 and 1.16). The use of a circular dichroism detector allows the elution order to be established in a non-empirical way. This information is then used to propose a chiral recognition mechanism.

An Insoluble Polymer‐Bound Bis‐Oxazoline Copper(II) Complex: A Highly Efficient Heterogeneous Catalyst for the Enantioselective Mukaiyama Aldol Reaction

The polystyrene-supported bis-oxazoline 1 forms a complex with copper(II)triflate that is a highly effective catalyst for the heterogeneously catalyzed enantioselective Mukaiyama aldol reaction of silylthioketene acetals with methyl pyruvate (ca. 90 % yield, ca. 90 % ee). The catalyst can be recovered by simple filtration and reused several times without a decline in enantioselectivity.

Heterogeneous Catalytic Asymmetric Dihydroxylation of Olefins with the OsO4/Poly(9-O-Acylquinine-co-Acrylonitrile) System

Abstract Heterogeneous catalytic asymmetric dihydroxylation of olefins has been achieved using, as chiral ligands of OsO4, the title insoluble polymeric derivatives of quinine.

Enantioselective alkylation of prochiral aldehydes by diethylzinc promoted by (S,S)-1,2-diphenylethan-1,2-diol

Abstract The title compound catalyzed reaction of diethylzinc with aromatic aldehydes provides optically active carbinols (e.e. up to 78%).

A reusable, insoluble polymer-bound bis(oxazoline) (IPB-box) for highly enantioselective heterogeneous cyclopropanation reactionsElectronic supplementary information (ESI) available: experimental. See http://www.rsc.org/suppdata/cc/b3/b306483b/

A reusable, insoluble polystyrene-supported bis(oxazoline) was developed, affording e.e.s > 90% in the heterogeneous enantioselective cyclopropanation of styrene and 1,1-disubstituted alkenes with ethyl diazoacetate.

Addition of diethylzinc to aryl aldehydes catalyzed by (1S,3S)-N,N1-bis[benzyl]-1,3-diphenyl-1,3-propanediamine and its dilithium salt: a mechanistic rationale investigation.

Abstract N,NI-bis-benzyl substituted 1,3-diamine 1a , synthesized in high optical purity, and the corresponding dilithium salt 1b are used, for the first time, as chiral catalysts in the addition of ZnEt2 to aromatic aldehydes. Both 1a and 1b are able to promote the reaction but the products obtained exhibited low enantiomeric excesses. By 1H NMR and UV-CD investigation, experimental evidences about the structure of some reaction intermediates have been gained: reaction pathway consistent with spectroscopic data, chemical and stereochemical results could be postulated.