GREEN CHEMISTRY…Reduction of amides without hydride reagents

New Drug Approvals

Clostridium sporogenes

Essentially all medicines and current drug candidates contain at least one basic nitrogen atom. A common approach to the synthesis of amines is to reduce the corresponding amide with a hydride reagent such as LiAlH4, DIBAL, RedAl, B2H6, Et3SiH, or polymethylhydroxysilane (PMHS).

The reaction survey reported that reduction of amides to amines was used in only 0.6% of chemical transformations; this number would surely be higher if safer methods for use on scale were available. The survey indicated that the number of amide reductions was equally split between diborane and hydride reagents.

Lithium aluminium hydride,

Wireframe model of lithium aluminium hydride

having a molecular weight of 38 and four hydrides per molecule, has the highest hydride density and is frequently used, even though it co-generates an inorganic by-product (lithium aluminum hydroxide) which is difficult to separate from the product. The workup procedure recommended by one bulk supplier…

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