Hemiaminal ethers preparation

Scheme 3.56 Preparation of hemiaminal ethers via addition of alcohols to imines.

Acid catalysed opening of the epoxide 47 in the presence of benzylamine afforded 6-ben lamino-l,4,6-trideoxy-l,4-imino-D-mannitol as product, whereas in the absence of ben lamine the rearranged fert-butyl ether 48 was the major isolate. The same paper also describes the preparation of the 7-membered ring product 49 by reacting bic clic hemiaminal 50 (prepared in six steps from benzyl-4-azido-4-deoxy-2,3-0-isopro idene-a-D-mannopyranoside) with sodium cyanoborohydride followed by hydrolysis. ... 

Synthetically important chiral 1-monosubstituted 1,3-diamines (145) are synthesized in Mannich-t)fpe reactions of enecarbamates (140) with aromatic and aliphatic hemiaminal ethers (141) in the presence of phosphoric acid 95a. This process involves the highly reactive Mannich-t)fpe product (144), which is entrapped by a methanol molecule generated during the formation of the imine (143) derived from the hemiaminal ether (141) (Scheme 28.15) [72]. Similarly, diastereo- and enantio-enriched anti-l,2-disubstituted 1,3-diamines are prepared by the Mannich-type reaction of aldehydes, anilines, and enecarbamates in the presence of chiral phosphoric acid [73]. 

The one-pot diphenylproHnol silyl ether 1 catalyzed Michael reaction of cro-tonaldehyde and nitroalkene arrives at the intermediate 247, which is followed by the an aza-Henry reaction/hemiaminalization process to a proposed alcohol intermediate, followed by Lewis acid-mediated allylation or cyanation (Scheme 7.54). A later report of polysubstituted piperidine 251 preparation was carried out through a Michael addition of 249 and 250 and an aminahzation reaction process, remarkably in water [123]. This process was also carried out to form tetrahydropyrans... 

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