Acyl fluorides transfer hydrogenation

Quantitative N-acylation of the terminal Hmb residue, even with the aid of the acyl transfer mechanism, requires special attention. As illustrated in Figure 4, an initial base-catalysed esterification occurs which is favoured through tautomer 4c. Optimal acylation occurs via symmetric anhydride (7) Protocol 4), urethane-A -carboxy anhydride (58), or pre-formed acid fluoride (59) in the apolar aprotic solvent dichioromethane, conditions which preserve the crucial hydrogen-bonded structure 4c. Typical acylation times are detailed in Table 1. 

---