What Is Chan Alkyne Reduction Reaction?
The Chan alkyne reduction, also referred to as the Red-Al-mediated alkyne reduction, is a stereoselective method for converting acetylenic alcohols (alkynols) into trans-(E)-allylic alcohols. Developed by chemist Ka-Kong Chan and coworkers, this reaction employs sodium bis(2-methoxyethoxy)aluminum hydride (SMEAH, commercially known as Red-Al) or lithium aluminum hydride (LiAlH4) as the reductant. Unlike conventional alkyne hydrogenations, the Chan reduction specifically targets alkynols and proceeds with high stereochemical fidelity to deliver E-configured allylic alcohols, making it invaluable in synthetic organic chemistry.
- Reagents: SMEAH (Red-Al) or LiAlH4; tetrahydrofuran (THF) or diethyl ether.
- Reactants: Alkynols (Substrates containing a hydroxyl (-OH) group adjacent to a carbon-carbon triple bond).
- Products: E-allylic alcohols.
- Reaction type: Stereoselective reduction.
- Related reactions: Birch reduction, Corey-Fuchs reaction, Lindlar hydrogenation.
- Experimental tips:
a) Red-Al and lithium aluminum hydride are both aluminum-containing reducing agents, but lithium aluminum hydride has low solubility in aromatic solvents, while red aluminum is soluble in aromatic solvents. Red-Al solution is a toluene solution containing 70% Red-Al. Red-Al solution is more stable than lithium aluminum hydride in moisture and air, and its thermal stability is also higher, and it can be heated to 200°C.
b) Using this Red-Al reducing agent, cyano groups can be reduced to aldehydes, epoxides can be reduced to alcohols, and the like.
Fig 1. Chan alkyne reduction reaction and its mechanism. [1]
Mechanism of Chan Alkyne Reduction
Red-Al first reacts with hydroxyl groups to transfer hydrogen within the molecule to generate alkenyl carbon anions, and then post-processes to obtain products.
The alkenyl aluminum formed during the reaction can react with various electrophilic reagents, so it can be converted into various desired compounds and has high utilization value. For example, if used in combination with DIBAL, a trans reduction product can be obtained.
Application Examples of Chan Alkyne Reduction
- Example 1: In the stereoselective synthesis routes of (+)-(6R,2'S)-cryptocaryalactone, chiral propargyl secondary hydroxy compound was chemoselectively reduced with LiAlH4 in tetrahydrofuran at 0 °C to afford cinnamyl alcohol derivative (87%). [2]
- Example 2: Tushar Kanti Chakraborty et al. reported a total synthetic route for (-)-clavosolide A. The 9R-stereoisomer was reduced with Red-Al to afford E-allyl alcohol in 80% yield. Subsequently, the expected syn-product was obtained as the major isomer in 91% yield (de >96%) under modified Simmons-Smith cyclopropanation conditions. [3]
- Example 3: Christopher T. Meta et al. used γ-hydroxy-α,β-alkynoic acid esters as precursors to prepare γ-hydroxy-α,β-enoate esters by trans-selective addition of two hydrogen atoms or one hydrogen atom and one iodine atom on the triple bond. In order to expand the application of trans-selective Red-Al-promoted conjugate addition reactions in acetylenic esters, the Red-Al-reduced intermediate alcohol was quenched with I2 instead of water to obtain (Z)-enoate (yield 78%). [4]
Fig 2. Synthetic examples via Chan alkyne reduction reaction.
Related Products
| CAS No. | Structure | Product | Inquiry |
| 142-30-3 |  | 2,5-Dimethyl-3-hexyne-2,5-diol | Inquiry |
| 126-86-3 |  | 2,4,7,9-Tetramethyl-5-decyne-4,7-diol (technical grade) | Inquiry |
| 1719-19-3 |  | 2-Methyl-4-phenyl-3-butyn-2-ol | Inquiry |
| 3031-66-1 |  | 3-Hexyne-2,5-diol | Inquiry |
| 50428-39-2 |  | 1,3-Dineopentylidyne-2-propanol | Inquiry |
| 78629-20-6 |  | 3-Hydroxy-6,6-Dimethyl-1-Heptene-4-Yne | Inquiry |
| 1522-13-0 |  | 1,1,3-Triphenylpropargyl alcohol | Inquiry |
| 74514-59-3 |  | 2-Octyn-4-ol, 4-methyl- | Inquiry |
| 71065-39-9 |  | 3-Methyl-4-heptyn-3-ol | Inquiry |
| 1002-36-4 |  | 2-Heptyn-1-ol | Inquiry |
| 105-31-7 |  | 1-Hexyn-3-ol | Inquiry |
| 109-50-2 |  | 3-Hexyn-2-ol | Inquiry |
References
- Jie Jack Li. Name Reactions-A Collection of Detailed Mechanisms and Synthetic Applications, Fourth Edition, 2014, 123-124.
- Krishna, Palakodety Radha, et al. Beilstein Journal of Organic Chemistry, 2009, 5(1), 14.
- Chakraborty, Tushar Kanti, et al. Tetrahedron, 2008, 64(22), 5162-5167.
- Meta, Christopher T., et al. Organic letters, 2004, 6(11), 1785-1787.
