Barton–McCombie deoxygenation

Barton–McCombie deoxygenation is a chemical reaction used in organic chemistry for the removal of oxygen atoms from molecules, specifically for converting alcohols into alkanes. This reaction is significant for its utility in the synthesis of complex organic molecules, including natural products and pharmaceuticals. The Barton–McCombie deoxygenation process involves the radical reduction of a hydroxyl group to a hydrogen atom, effectively replacing the oxygen in an alcohol with hydrogen to produce an alkane.

Mechanism

The mechanism of the Barton–McCombie deoxygenation involves several key steps. Initially, the alcohol is converted into a thiohydroxamate ester by reaction with a thiocarbonyl compound, such as a thiocarbonyl chloride. This ester is then subjected to radical conditions, typically using a radical initiator like tributyltin hydride (Bu3SnH) and a radical promoter such as AIBN (azobisisobutyronitrile). The radical initiator abstracts a hydrogen atom from the thiohydroxamate, generating a radical intermediate. This intermediate undergoes fragmentation, expelling a thiocarbonyl compound and forming a carbon-centered radical. Finally, this radical is reduced by a second molecule of tributyltin hydride, yielding the deoxygenated alkane product.

Applications

The Barton–McCombie deoxygenation reaction is widely used in organic synthesis for the preparation of deoxygenated molecules, which are often key intermediates in the synthesis of natural products, pharmaceuticals, and other complex organic compounds. Its ability to selectively remove oxygen atoms from specific positions within a molecule makes it a valuable tool for chemists designing synthetic routes to complex targets.

Advantages and Limitations

One of the main advantages of the Barton–McCombie deoxygenation is its high selectivity and the ability to preserve sensitive functional groups elsewhere in the molecule. However, the use of toxic reagents like tributyltin hydride and the generation of tin byproducts, which are environmentally hazardous, pose significant limitations. Recent advancements have focused on developing more environmentally friendly alternatives, including the use of silanes and other non-toxic reducing agents.

See Also

• Deoxygenation
• Radical chemistry
• Organic synthesis
• Thiocarbonyl compound

External Links

• Barton–McCombie deoxygenation on Organic Chemistry Portal