Zhi-Min Chen

Organocatalytic asymmetric halogenation/semipinacol rearrangement: highly efficient synthesis of chiral α-oxa-quaternary β-haloketones.

A novel asymmetric halogenation/semipinacol rearrangement reaction catalyzed by cinchona alkaloid derivatives was developed. Two types of β-haloketones (X = Br, Cl) were obtained with up to 95% yield and 99% enantiomeric excess. The desired (+) and (-) enantiomers of the β-haloketones were readily obtained.

Enantioselective bromination/semipinacol rearrangement for the synthesis of β-bromoketones containing an all-α-carbon quaternary center

A bromination/semipinacol rearrangement reaction catalyzed by cinchona alkaloid derivatives was developed. With 5 mol% (DHQD)2PYDZ, β-bromoketones containing an all-α-carbon quaternary center, which were synthetically useful but challenging to construct, were obtained in up to 97% yield and 93% ee.

Total Synthesis of (±)-Maistemonine, (±)-Stemonamide, and (±)-Isomaistemonine

A full account of the total synthesis of (±)-maistemonine, (±)-stemonamide, and (±)-isomaistemonine is presented. Two approaches have been developed to construct the basic pyrrolo[1,2-a]azepine core of the Stemona alkaloids, featuring a tandem semipinacol/Schmidt rearrangement of a secondary azide and a highly stereoselectively desymmetrizing intramolecular Schmidt reaction, respectively. To build the common spiro-γ-butyrolactone, a new protocol was carried out by utilizing an intramolecular ketone-ester condensation as the key transformation. The vicinal butyrolactone moiety of (±)-maistemonine was stereoselectively introduced via a one-pot procedure involving the epimerization at C-3 and carbonyl allylation/lactonization. Moreover, (±)-stemonamide was divergently synthesized from a common intermediate, and (±)-isomaistemonine was obtained via the epimerization of (±)-maistemonine at C-12.

Organocatalytic asymmetric fluorination/semipinacol rearrangement: an efficient approach to chiral β-fluoroketones.

An asymmetric fluorination/semipinacol rearrangement of 2-oxa allylic alcohols, as catalyzed by cinchona-alkaloid derivatives, gives chiral β-fluoro ketones with moderate to high levels of enantioselectivity (see scheme). Both enantiomers of the product could be obtained by using the appropriate catalyst.

Palladium-Catalyzed Enantioselective Redox-Relay Heck Arylation of 1,1-Disubstituted Homoallylic Alcohols

An enantioselective redox-relay oxidative Heck arylation of 1,1-disubstituted alkenes to construct β-stereocenters was developed using a new pyridyl-oxazoline ligand. Various 1,2-diaryl carbonyl compounds were readily obtained in moderate yield and good to excellent enantioselectivity. Additionally, analysis of the reaction outcomes using multidimensional correlations revealed that enantioselectivity is tied to specific electronic features of the 1,1-disubstituted alkenol and the extent of polarizability of the ligand.

Palladium-Catalyzed Enantioselective Redox-Relay Heck Alkynylation of Alkenols To Access Propargylic Stereocenters

An enantioselective redox-relay Heck alkynylation of di- and trisubstituted alkenols to construct propargylic stereocenters is disclosed using a new pyridine oxazoline ligand. This strategy allows direct access to chiral β-alkynyl carbonyl compounds employing allylic alcohol substrates in contrast to more traditional conjugate addition methods.

Total Synthesis of (+/-)-Parvineostemonine

Roots and rhizomes of the stemonaceous plant have long been used for the treatment of respiratory diseases and as domestic insecticides in traditional folk medicine of East Asia. So far, over 130 structurally diverse Stemona alkaloids have been isolated from the monocotyledonous family Stemonaceae. These Stemona alkaloids have fascinating architectures and potential biological activities, which have provoked broad interests in their total synthesis. Among the Stemona alkaloids, parvineostemonine (1a), isolated from Stemona parviflora by Ye and co-workers in 2003, is a unique molecule which differs from the typical Stemona alkaloids such as 1b–1e (Figure 1). Parvineostemonine fea-

Electrophilic Trifluoromethylthiolation/Semipinacol Rearrangement: Preparation of β-SCF3 Carbonyl Compounds with α-Quaternary Carbon Center

A new and modular electrophilic trifluoromethylthiolation/semipinacol rearrangement of allylic silyl ethers has been developed under mild conditions. This approach allows the formation of a number of β-SCF3 carbonyl compounds with a cyclic and all-carbon quaternary center framework in moderate to good yields. It should be noted that this achievement is a metal-free process and just requires the use of simple acetyl chloride as an acidic promoter. Additionally, an interesting H-migration in competition with aryl-migration process was revealed.

CCDC 821778: Experimental Crystal Structure Determination

Related Article: Hui Li, Fu-Min Zhang, Yong-Qiang Tu, Qing-Wei Zhang, Zhi-Min Chen, Zhi-Hua Chen, Jian Li|2011|Chemical Science|2|1839|doi:10.1039/c1sc00295c