Protecting amines with

So, where is the safety catch The important point about Fmoc is that is has a rather acidic proton (p Ca about 25), shown in black. The proton is the Achilles heel treatment of Fmoc-protected amines with base eliminates a fulvene to reveal the NH2 group. 

Based on the aforementioned examples, it is the facile removal of the nosyl protecting group developed by Fukuyama that makes this methodology useful. Treatment of a nosyl protected amine with a variety of thiols, or other nucleophiles, gives the Meisenheimer complex 12. Upon loss of SO2, this generates the desired secondary amine 5 along with a thioether 13a-c which must be removed. 

Figure 17 Formation of dibenzofulvene-piperidine adduct by treatment of an Fmoc-protected amine with piperidine.

KHMDS was shown to be as effective as LHMDS in the boron-assisted displacement of secondary chloride which led to the corresponding protected amine with inversion of configuration (eq 26). The chemoselective displacement of the chloride is greatly facilitated by the a-boro substituent, which is known to cause a rate acceleration on the attack of nucleophiles of approximately two orders of magnitude relative to the primary halide. ... 

While the hydroamination of ethylene with simple amines has been investigated experimentally and computationally over the past few years, the limited success realized and the significant challenge of this reaction have pointed toward the utility of protected amines with reduced nucleophilidty. Early results from the Widenhoefer group [158] showed that [PtCl2(C2H4)]2 combined with simple phosphine Hgands can mediate the hydroamidation and hydrocarbamation of ethylene at less than 4 bar of ethylene pressure at 120 °C (Table 15.12). 

The conjugate addition reactions of a-aminoalkylcuprates (derived from r-butoxy-carbonyl protected amines) with Q, /3-/3,y-allenyl esters occurs with preferred approach from the side opposite the substituent on the 4-position and results in trans alignment of the respective groups about the unconjugated double bond on the 1,4-adduct (Scheme 11). ... 

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