Alessandro Mandoli

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.

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.

A chiral organocatalytic polymer-based monolithic reactor

Radical copolymerisation of divinylbenzene and a properly modified enantiomerically pure imidazolidinone inside a stainless steel column in the presence of dodecanol and toluene as porogens afforded the first example of a chiral organocatalyst immobilized onto a monolithic reactor. Organocatalyzed cycloadditions between cyclopentadiene and cinnamic aldehyde were performed under continuous-flow conditions; by optimizing the experimental set up, excellent enantioselectivities (90% ee at 25 °C) and high productivities (higher than 330) were obtained, thus showing that a catalytic reactor may work efficiently to continuously produce enantiomerically enriched compounds. The same catalytic reactor was also employed to carry out three different stereoselective transformations in continuo, sequentially, inside the chiral column (Diels–Alder, 1,3-dipolar nitrone-olefin cycloaddition, and Friedel–Crafts alkylation); excellent results were obtained in the case of the former two reactions (up to 99% yield, 93% ee and 71% yield, 90% ee, at 25 °C, respectively). In addition to simplify the product recovery, the monolithic reactor performed better than the same supported organocatalyst in a stirred flask and could be kept working continuously for more than 8 days.

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.

Heterogeneous asymmetric catalytic aminohydroxylation promoted by a bis-Cinchona alkaloid derivative supported onto an insoluble organic polymeric matrix

Abstract By using a bis(quinidinyl)phthalazine derivative linked to an insoluble organic polymer, 87% e.e. was obtained in the osmium-mediated catalytic heterogeneous asymmetric aminohydroxylation of isopropyl trans -cinnamate. The recycling of the polymeric ligand–osmium complex was also investigated.

A first example of macromolecular Ti(IV) Lewis acid in the catalytic enantioselective Mukaiyama reaction

Abstract The preparation and characterization of a soluble copolymer P1 between styrene, divinylbenzene (DVB) and the enantiomerically pure salicylaldimine ligand 3c is described. The Lewis acid prepared from this macromolecular chiral ligand and Ti(OiPr)4 has been used in the catalytic Mukaiyama reaction to afford benzyl (R)-3-hydroxy-3-phenylpropanoate 7.

A Catalytic Reactor for the Organocatalyzed Enantioselective Continuous Flow Alkylation of Aldehydes

The use of immobilized metal-free catalysts offers the unique possibility to develop sustainable processes in flow mode. The challenging intermolecular organocatalyzed enantioselective alkylation of aldehydes was performed for the first time under continuous flow conditions. By using a packed-bed reactor filled with readily available supported enantiopure imidazolidinone, different aldehydes were treated with three distinct cationic electrophiles. In the organocatalyzed α-alkylation of aldehydes with 1,3-benzodithiolylium tetrafluoroborate, excellent enantioselectivities, in some cases even better than those obtained in the flask process (up to 95% ee at 25 °C), and high productivity (more than 3800 h(-1) ) were obtained, which thus shows that a catalytic reactor may continuously produce enantiomerically enriched compounds. Treatment of the alkylated products with Raney-nickel furnished enantiomerically enriched α-methyl derivatives, key intermediates for active pharmaceutical ingredients and natural products.

Enantioselective synthesis and CD assignment of absolute configuration of (−)-1,3-diphenylpropane-1,3-diol

Abstract Highly stereoselective hydrogenation of dibenzoylmethane in the presence of [RuCl 2 {(R)-biphemp}] [biphemp = 2,2′-bis(diphenylphosphino)-6,6′-dimethyl-1,1′-biphenyl], in ethanol-dichloromethane, gives enantiomerically pure (−)-1,3-diphenylpropane-1,3-diol ( 2 ) (70% yield); analysis of the CD spectra of the corresponding acetonide allows the absolute configuration of the diol to be established as (S,S). The direct HPLC separation of the enantiomers of ( 2 ) is also reported.

A new class of optically active pyrrole derivatives: (3R)-3-(pyrrol-1-yl)alk-1-enes from d-α-aminoacids

Abstract (3 R )-3-(Pyrrol-1-yl)but-1-ene 4a , (3 R )-4-methyl-3-(pyrrol-1-yl)pent-1-ene 4b , (3 R )-3-(pyrrol-1-yl)hex-1-ene 4c in high enantiomeric excess (>92%) were prepared starting from d -α-amino acids. The crucial steps in the synthesis, reduction (DIBAH) of the corresponding pyrrolylesters to the corresponding pyrrolylaldehydes followed by Wittig olefination proceeded without compromising the stereochemical integrity.

Pyriculins A and B, two monosubstituted hex‐4‐ene‐2,3‐diols and other phytotoxic metabolites produced by Pyricularia grisea isolated from buffelgrass (Cenchrus ciliaris)

Pyricularia grisea has been identified as a foliar pathogen on buffelgrass (Cenchrus ciliaris) in North America and was studied as a potential source of phytotoxins for buffelgrass control. Two monosubstituted hex-4-ene-2,3-diols, named pyriculins A and B, were isolated from its culture filtrate organic extract together with (10S,11S)-(-)-epipyriculol, trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-napthalenone, and (4S)-(+)-isosclerone. Pyriculins A and B were characterized by spectroscopic (essentially nuclear magnetic resonance [NMR], High-resolution electrospray ionization mass spectrometry [HRESIMS]) and chemical methods such as (4E)-1-(4-hydroxy-1,3-dihydroisobenzofuran-1-yl)hex-4-ene-2,3-diols. The relative and absolute configuration of these compounds was determined by a combination of spectroscopic (NMR, electronic circular dichroism [ECD]) and computational tools. When bioassayed in a buffelgrass coleoptile and radicle elongation test, (10S,11S)-(-)-epipyriculol proved to be the most toxic compound. Seed germination was much reduced and slowed with respect to the control and radicles failed to elongate. All five compounds delayed germination, but only (10S,11S)-(-)-epipyriculol was able to prevent radicle development of buffelgrass seedlings. It had no effect on coleoptile elongation, while the other four compounds caused significantly increased coleoptile development relative to the control.