Chunling Fu

Highly Selective Mild Stepwise Allylation of N-Methoxybenzamides with Allenes

An efficient Rh(III)-catalyzed stepwise ortho allylation of N-methoxybenzamides 1 with polysubstituted allenes is reported. This C-H functionalization involving allenes is conducted under very mild conditions (-20 °C or room temperature) and compatible with ambient air and moisture, and it can be applied to terminal or internal allenes with different synthetically attractive functional groups. Highly efficient axial chirality transfer has been realized, yielding optically active lactones.

Room-Temperature Synthesis of Trisubstituted Allenylsilanes via Regioselective C–H Functionalization

A Rh(III)-catalyzed o-C-H bond functionalization-based allenylation reaction of allenylsilanes 2 with N-methoxybenzamides 1 affords poly-substituted allenylsilanes with a wide range of attractive functional groups in moderate to excellent yields under very mild conditions (20 °C, compatible with ambient air and moisture). Those products may be transformed to different products with attractive structural features. Careful mechanistic studies suggest the reaction proceeds via o-rhodation, regioselective insertion, and β-H elimination.

An efficient synthesis of carbazoles from PtCl2-catalyzed cyclization of 1-(indol-2-yl)-2,3-allenols

The PtCl(2)-catalyzed reaction of 1-(indol-2-yl)-2,3-allenols occurred smoothly to form carbazoles by connecting the 3-carbon atom of indole with the 4-carbon atom of the allenol moiety, referring to the carbon atom connected to the hydroxyl group.

Carbazoles via AuCl3-Catalyzed Cyclization of 1-(Indol-2-yl)-3-alkyn-1-ols

AuCl(3)-catalyzed reaction of 1-(indol-2-yl)-3-alkyn-1-ols occurred smoothly in toluene at room temperature to form a benzene ring leading to a series of carbazole derivatives efficiently. A possible mechanism has been proposed for the formation of carbazoles.

Synthesis of Polysubstituted Furans Based on a Stepwise Sonogashira Coupling of (Z)-3-Iodoalk-2-en-1-ols with Terminal Propargylic Alcohols and Subsequent Au(I)- or Pd(II)-Catalyzed Cyclization−Aromatization via Elimination of H2O

Recently, we have developed highly regio- and stereoselective carbometalation of 2-alkynols and 2,3-allenols. The organometallacyclic intermediates may be trapped with I(2) to afford 3-iodoalk-2-en-1-ols. These 3-iodoalk-2-en-1-ols may readily undergo the Sonogashira coupling with terminal propargyl alcohols to form 4-alkyn-2-ene-1,6-diols. Subsequent cycloisomerization in DMA or CH(2)Cl(2) with Au(PPh(3))Cl and AgOTf as the catalyst would afford polysubstituted 2-(1-alkenyl)furans; with PdCl(2) as the catalyst and the reaction in DMA in the presence of allylic bromides, the same substrates afforded polysubstituted 2-(1,4-alkadienyl)furans. In both types of catalyzed cyclization reactions, the elimination of H(2)O promoted the aromatization to form the furan ring. Different alkyl or aryl groups could be introduced into different positions of furans due to the substituent-loading capability of 3-iodoalkenols and diversity of the terminal propargyl alcohols and allylic bromides.

A C–H bond activation-based catalytic approach to tetrasubstituted chiral allenes

Enantioselective synthesis of fully substituted allenes has been a challenge due to the non-rigid nature of the axial chirality, which spreads over three carbon atoms. Here we show the commercially available simple Rh complex may catalyse the CMD (concerted metalation/deprotonation)-based reaction of the readily available arenes with sterically congested tertiary propargylic carbonates at ambient temperature affording fully substituted allenes. It is confirmed that the excellent designed regioselectivity for the C–C triple bond insertion is induced by the coordination of the carbonyl group in the directing carbonate group as well as the steric effect of the tertiary O-linked carbon atom. When an optically active carbonate was used, surprisingly high efficiency of chirality transfer was realized, affording fully substituted allenes in excellent enantiomeric excess (ee).

PtCl4-Catalyzed Cyclization Reaction of β-Allenols in the Presence of Indoles

The highly regioselective PtCl4-catalyzed reaction of indoles with beta-allenols in THF at room temperature afforded indole derivatives containing a six-membered ether ring at the 3-position in moderate isolated yields. On the basis of a D-labeling experiment, a mechanistic rationale was proposed.

A novel synthesis of 1,3-oxazine-2,4-diones via a simple and efficient reaction of CO2 with 2,3-allenamides.

A simple and efficient reaction of CO(2) with 2,3-allenamides under mild conditions (CO(2) balloon without any metal catalyst in the presence of K(2)CO(3) or Cs(2)CO(3)) leads to an efficient synthesis of 1,3-oxazine-2,4-diones. The high reactivity of the allene moiety is crucial for the success of this transformation since the corresponding reaction of alpha,beta-unsaturated alkenamides or alkynamides does not occur.

Efficient assembly of chromone skeleton from 2,3-allenoic acids and benzynes.

Chromone derivatives were synthesized from 2,3-allenoic acids and benzynes in moderate to excellent yields under mild conditions. Instead of the cyclic conjugate addition of the intermediate A formed by the nucleophilic addition of allenoic acid with benzyne, this intermediate undergoes 1,2-addition with the carbonyl group, which was followed by the ring opening, conjugate addition, and protonolysis to afford chromone derivatives. This protocol allows the diversity due to the substituent-loading capability of 2,3-allenoic acids as well as benzynes.

A General Diversified Synthesis of Carbazoles and the First Synthesis of Karapinchamine A

[IPrAuCl]/AgSbF6 -catalyzed cyclization of the readily available 4-benzoxyl-1-(indol-2-yl)-2-alkynols occurred smoothly in 1,2-dichloroethane (DCE) in the presence of 4 Å MS to form a series of differently polysubstituted 2-oxygenated carbazole derivatives efficiently. Based on mechanistic study, a possible mechanism involving 1,3-migration of a benzoate group to form the allene, Au(+) -mediated cyclization-elimination to form a gold-carbene intermediate, and subsequent highly selective 1,2-migration has been proposed for the formation of carbazoles. Highly selective 1,2-migration referring to the two substituents R(3) and R(4) (R(4) =H, alkyl, and aryl group) was observed: (1) In the presence of both H and alkyl groups, 1,2-hydrogen migration is exclusive; (2) in the presence of a methyl group (R(3) ), propyl, isopropyl, 4-methylphenyl, and 4-chlorophenyl groups (R(4) ) migrate exclusively. Finally, the first total synthesis of the recently isolated naturally occurring carbazole alkaloid karapinchamine A in 5.2 g scale has been realized in 6 steps from commercially available chemicals without need for any protection-deprotection.