Conversion of Alcohols into Alkanes

• General Characteristics

Direct reduction of alcohols to alkanes is generally difficult. The conversion usually requires a two-step sequence involving the conversion of alcohols into leaving groups (such as halides and sulfonate esters) followed by reduction with metal hydrides (such as LiAlH₄, LiHBEt₃, Bu₃SnH + radical initiator). There are also other classical methods for reductive removal of halides such as heterogeneous hydrogenation and the Birch reduction.

The reagents such as PX₃, PX₅, SOCl₂, and (COCl)₂ provide easy ways for the halogenation step. The Appel conditions are suited when one needs to do the halogenation under neutral conditions. For the sulfonation, MsCl-Et₃N and TsCl-Py(-DMAP) are the typical conditions used.

The reduction of alcohols except for aliphatic primary alcohols is known using LiAlH₄-AlCl₃ (1:3), but the carbocationic intermediates are potentially prone to undesired rearrangements and isomerizations.

The reduction of primary alcohols using NaBH₃CN-(PhO)₃PCH₃I is sometimes used, in which the alkyl iodides formed in situ are reduced in the same pot.

In the popular Barton-McCombie deoxygenation, hydroxyl groups are removed under free-radical based conditions.

• General References

• Reaction Mechanism

The mechanism can be regarded as nucleophilic displacement by the hydride (for the reactions using metal hydrides).

• Examples

• Experimental Procedure

• Experimental Tips

• References

• Related Books

deoxygenation of alcohols, reductive removal of hydroxyl groups, synthesis of alkanes