Aijun Lin

Organocatalyzed Asymmetric 1,6-Conjugate Addition of para-Quinone Methides with Dicyanoolefins

A chiral thiourea catalyzed asymmetric 1,6-conjugate addition of para-quinone methides with dicyanoolefins has been developed. The reaction provided an efficient approach to the synthesis of chiral diarylmethine skeletons in good yields (up to 99% yield) with high diastereo- and enantioselectivity (>20:1 dr and up to 99.5:0.5 er), also on a gram scale. The preliminary mechanistic study showed that the remote stereocontrol was achieved through intermolecular hydrogen-bond interaction between the chiral thiourea catalyst and the para-quinone methides directly for the first time.

Organocatalytic oxa/aza-Michael–Michael Cascade Strategy for the Construction of Spiro [Chroman/Tetrahydroquinoline-3,3′-oxindole] Scaffolds

A new useful and effective chiral amine-catalyzed oxa- and aza-Michael-Michael cascade methodology for the construction of enantiomerically enriched indolinones spiro-fused with chromans or tetrahydroquinolines is reported. By employing suitable organocatalysts depending on the different Michael donors (Ar-OH/Ar-NHR), the processes offered excellent stereocontrol (dr >20:1, >99% ee) under mild conditions.

Solvent-controlled Switchable C-H Alkenylation of 4-Aryl 1H-pyrrole 3-carboxylates: Application to the Total Synthesis of (±)-Rhazinilam

A solvent-controlled switchable C-H alkenylation of 4-aryl-1H-pyrrole-3-carboxylates via a Pd(OAc)2 catalyzed oxidative Heck reaction was first realized. The corresponding C2 and C5 alkenylation products were obtained in good yields with high regioselectivities, respectively. The selective C5-alkenylation was successfully applied to the total synthesis of (±)-rhazinilam.

1,6-Conjugated Addition-Mediated [2+1] Annulation: Approach to Spiro[2.5]octa-4,7-dien-6-one

A formal 1,6-conjugated addition-mediated [2+1] annulation to synthesize spiro[2.5]octa-4,7-dien-6-one with p-quinone methides and sulfur ylides has been described. This domino-type process was highly diastereoselective and exhibited good functional group tolerance and scalability without the use of metals and bases.

Bifunctional Organo/Metal Cooperatively Catalyzed [3 + 2] Annulation of para-Quinone Methides with Vinylcyclopropanes: Approach to Spiro[4.5]deca-6,9-diene-8-ones

A novel [3 + 2] annulation between para-quinone methides and vinylcyclopropanes for the synthesis of spiro[4.5]deca-6,9-diene-8-ones has been described. The palladium and phosphine-thiourea cooperative catalysis system played an important role in high yields and diastereoselectivities. The reaction exhibited good functional group tolerance and scalability.

N-Indolyltriethylborate: A Useful Reagent for Synthesis of C3-Quaternary Indolenines

N-Indolyltriethylborate was found to be a useful reagent for dearomatizing C3-alkylation of 3-substituted indoles with both activated and nonactivated alkyl halides to give C3-quaternary indolenines, pyrroloindolines, furoindoline, and hexahydropyridoindoline under mild reaction conditions. The utility of these reagents was demonstrated in the syntheses of a pyrroloindoline-4-cholestene hybrid and debromoflustramine B.

Rh(III)-Catalyzed Redox-Neutral Annulation of Primary Benzamides with Diazo Compounds: Approach to Isoquinolinones

Reported herein is a Rh-catalyzed redox-neutral annulation of primary benzamides with diazo compounds, representing an efficient and economic protocol to isoquinolinones. The procedure exhibited good functional group tolerability, scalability, and regioselectivity, obviating the need for oxidants, and only environmentally benign N2 and H2O were released. Further utilization of the method provided an alternative route to functionalized isoquinolines.

Chiral Tertiary Amine Thiourea-Catalyzed Asymmetric Inverse-Electron-Demand Diels–Alder Reaction of Chromone Heterodienes Using 3-Vinylindoles as Dienophiles

A straightforward and efficient protocol for the construction of structurally and biologically interesting chiral flavanoids incorporating three privileged structures, i.e., chromanone, dihydropyran, and indole, has been developed on the basis of chiral bifunctional tertiary amine thiourea-catalyzed asymmetric inverse-electron-demand Diels-Alder reaction of chromone heterodienes and 3-vinylindoles, which were used as dienophiles.

Enantioselective Synthesis of Polycyclic Coumarin Derivatives Catalyzed by an in Situ Formed Primary Amine-Imine Catalyst

A facile in situ formed primary amine-imine organocatalyst was developed in the asymmetric Michael addition of substituted 4-hydroxycoumarins to cyclic enones. A series of optically active polycyclic coumarin derivatives were obtained in high yields with excellent enantioselectivities up to 97% ee.

Recent advances in C–H fluorination

Incorporation of fluorine atom(s) into organic compounds is often desirable in the discovery of new pharmaceuticals, agrochemicals, and materials. However, development of transformations to incorporate fluorine is challenging because of its highly electronegative nature. Recent advances in C–H functionalization have allowed new approaches to C–F bonds. Herein we highlight progress in C–H fluorination, which is arguably the most efficient approach to incorporate fluorine since it obviates the need of pre-functionalization of organic compounds.