Amino acids are nature's premier synthetic building blocks for bioactive molecules. Alongside the standard proteinogenic amino acids are diverse non-canonical amino acids (ncAAs) that are structurally similar but contain unnatural functional groups that confer novel chemical properties. These ncAAs function as precursors to natural products and are useful synthetic building blocks found in 12% of the 200 top-grossing pharmaceuticals. Of special interest are β-branched ncAAs that possess a second chiral center at the β-position in addition to the chirality typically found at the α-position (FIG. 1A). The two adjacent stereocenters impose conformational constraints that affect the biochemical properties of both the amino acids themselves and the molecules that incorporate them, making β-branched ncAAs frequent components of useful natural products, biochemical probes, and therapeutics (FIG. 1B). Despite their broad utility, most β-branched ncAAs are not readily available due to the challenge of forming two adjacent stereocenters while tolerating the reactive functional groups present in amino acids. For example, traditional organic synthesis of β-methyltryptophan requires multiple steps that incorporate protecting groups, hazardous reagents, and expensive metal catalysts. To take full advantage of these bioactive molecules, a more efficient methodology is needed to synthesize β-branched ncAAs.