Deprotection, by hydrogen

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

When the peptide synthesis was complete, the phosphines were deprotected by sequential treatment with MeOTf and HMPT (Scheme 36.9). Addition of the rhodium precursor then created the catalyst library, which was screened, on the pin in the enantioselective hydrogenation of methyl-2-acetamidoacrylate (see Scheme 36.10). Unfortunately, this beautiful concept was poorly rewarded with rather low enantioselectivities. 

The protecting group is removed by hydrogenation. The deprotected hydroxymethyl groups are used as initiators for polymerization of new e-CL. The process was repeated to the third generation to give a narrow molecular weight... 

FIGURE 3.5 Deprotection of functional groups by acidolysis.5 Protonation followed by car-bocation formation during the removal of benzyl-based protectors by hydrogen bromide. Two mechanisms are involved in generating benzyl bromide from the protonated substrates. 

FIGURE 3.6 Deprotection of functional groups by acidolysis. Protonation followed by carbocation formation during the removal of ferf-butyl-based protectors by hydrogen chloride.8 One mechanism is involved in generating the ferf-butyl cation, which is the precursor of two other molecules. 

The popular acids for deprotection by acidolysis are hydrogen fluoride for benzyl-based protectors and trifluoroacetic acid for rerr-butyl-based protectors. The use of hydrogen fluoride for deprotection emerged from the observation that it is a good solvent for dissolving enzymes (because of the N-to-0 acyl shift see Section 6.6), and that the enzymatic activity is recovered (O-to-N acyl shift) in saline solution. Two different approaches are employed for removal of benzyl-based... 

The synthesis of the module is provided in Scheme 10.5 (Kushner et al. 2007). Double alkylation of ethyl acetoacetate followed by guanidine condensation afforded alkenyl-pyrimidone intermediate 24 (Kushner et al. 2007). Isocyanate 25 was coupled to pyrimidone 24 to yield 26. Upon dimerization in DCM, RCM effectively cyclized the two UPy units (Mohr et al. 1997 Week et al. 1999). A one-pot reduction and deprotection through hydrogenation using Pearlman s catalyst gave diol module 27. Finally, capping 27 with 2-isocyanatoethyl methacrylate at both ends provided the UPy sacrificial cross-linker 28, which was thoroughly characterized by H- and C-NMR, Fourier transform IR (FTIR), and mass spectrometry. 

---