Alternatively, reductive amination allows installation of the second amine, furnishing both diastereomers of diamine 101 and 102, which are rather difficult to synthesize (previously requiring 23 steps). Although concise syntheses specific to 99 (4 steps) and 2 (2 steps) are known, those conventional approaches may be difficult to employ in more complex settings. For instance, in a molecule such as DAHD (3), the advantage of chemoselective decarboxylative acylation becomes apparent. The previous route to access this natural product begins from Garner's aldehyde (with questionable long-term stability), which is a rather expensive starting material that can be synthesized in 3 steps from serine. Since the terminal amino acid cannot be tolerated during the first Grignard addition, it was necessary to construct this motif separately in the synthesis. This chemoselectivity issue required many concession steps including expensive asymmetric hydrogenation, resulting in an 8-step synthesis (29% overall yield). In contrast, since the amino acid is compatible in decarboxylative acylation, 3 was synthesized in a single flask operation through sequential reagent addition (no intermediate solvent swap, workup, or removal of solvent, see SI for graphical procedure): simple attachment of aminoalcohol cassette to L-Boc-Glu-O t Bu followed by diastereoselective reduction and deprotection in 43% overall yield.