Protective removal, selective

Solvents exert control on the chemose-lective hydrogenation of alkenes bearing a benzyloxy protecting group [160]. In the unpolar solvent benzene, only the double bond is hydrogenated, while in methanol, acetone, and ethyl acetate, the benzyloxy group is also removed. Selective... 

Protected primary allylic amines were generated from allylic carbonates and ammonia equivalents. Iridium-catalyzed allylic substitution has now been reported with sulfonamides [90, 91], imides [89, 91-93], and trifluoroacetamide [89] to form branched, protected, primary allylic amines (Table 5). When tested, yields and selectivities were highest from reactions catalyzed by complexes derived from L2. Reactions of potassium trifluoroacetamide and lithium di-tert-butyhminodi-carboxylate were conducted with catalysts derived from the simplified ligand L7. Reactions of nosylamide and trifluoroacetamide form singly-protected amine products. The other ammonia equivalents lead to the formation of doubly protected allylic amine products, but one protecting group can be removed selectively, except when the product is derived from phthalimide. 

The protective group can be removed by reaction of a catalytic amount of Pdp QHs) and excess dimethyl malonate. This transfer reaction does not affect usual protective groups. On the other hand, the acetyl groups can be removed selectively by hy-drazinolysis. 

The reagent used to introduce the trimethylsilyl group is inexpensive. Protection of the alcohol function prior to silylation is unnecessary since the TMS group can in this case be removed selectively. 

A new carboxy protecting group that takes advantage of the facile solvolysis of cyclopropyl methyl substrates was proposed by Carpino et al.f The dicyclopropylmethyl (Dicyc-propme) ester can be used for carboxylic acid protection where selective removal is required in the presence of tBu or Trt side-chain protection. The ester is stable toward conditions of... 

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