C1C2C(CO[C:16]([NH:18][C@H:19]([C:24]([OH:26])=[O:25])[CH2:20][CH:21]([CH3:23])[CH3:22])=O)C3C(=CC=CC=3)C=2C=CC=1.C=O.FC(F)(F)C(O)=O.C([SiH](CC)CC)C>C1(C)C=CC=CC=1.C1(C)C=CC(S(O)(=O)=O)=CC=1>[CH3:16][NH:18][C@H:19]([C:24]([OH:26])=[O:25])[CH2:20][CH:21]([CH3:23])[CH3:22]
A suspension of N-[(9H-fluoren-9-ylmethoxy)carbonyl]-L-leucine (1.67 g, 5 mmol) in toluene(100 ml) was charged with paraformaldehyde (1 g, 33.3 mmol) and 4-toluenesulfonic acid (100 mg, catalytic). The mixture was refluxed for 30 minutes in a Dean Stark apparatus for azeotropic distillation. The solution was washed with a saturated solution of sodium bicarbonate (×2), dried over magnesium sulfate and evaporated. The resulting oil in a 1:1 mixture of chloroform:trifluoroacetic acid (50 ml), at room temperature, was charged with triethylsilane (2.38 ml, 15 mmol). Stirring was continued for 22 hr. The solvents were removed in vacuum and the oil was crystallized from a mixture of ether:hexane. Recrystalyzation from EtOAc:hexane afforded 0.85 g (46%) of the product as a colorless solid, mp 101°-3° C.
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