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Mannich Reactions with Amino Alcohols
Author(s) -
Schmidt Christian,
Straub Thomas,
Falàbu Dezsö,
Paulus Erich F.,
Wegelius Elina,
Kolehmainen Erkki,
Böhmer Volker,
Rissanen Kari,
Vogt Walter
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200012)2000:23<3937::aid-ejoc3937>3.0.co;2-x
Subject(s) - chemistry , intramolecular force , hydrogen bond , alkyl , crystal structure , stereochemistry , formaldehyde , nuclear magnetic resonance spectroscopy , mannich reaction , condensation reaction , condensation , medicinal chemistry , crystallography , organic chemistry , molecule , catalysis , physics , thermodynamics
The condensation of resorcarenes 1 with various amino alcohols and an excess of formaldehyde was studied. The tetrabenzoxazines 2a−e were found as the only products in the reaction with 6‐aminohexan‐1‐ol, 4‐aminobutan‐1‐ol, and 2‐aminoethanol, while 3‐aminopropan‐1‐ol forms the tetraoxazine 3 as the main product. In the case of aminoethanols substituted at the 2‐position with alkyl groups, the tetraoxazolidines 4 are the preferred reaction products, while 1‐methyl aminoethanol (1‐amino‐propan‐2‐ol) yields predominantly the tetrabenzoxazine 2f . The structures of all these compounds have been confirmed by NMR spectroscopy and additionally by single‐crystal X‐ray analysis in the case of 2a and 4b . In [D 6 ]DMSO, up to 60% of the corresponding, more polar tetrabenzoxazine structure is detected for compounds 3 and 4 , while the equilibrium is shifted to the less polar tetraoxazine or tetraoxazolidine in CDCl 3 . Low‐temperature NMR spectra show a C 4 ‐symmetrical conformation for the tetraoxazolidines 4 in CDCl 3 owing to intramolecular OH ··· OH ··· N hydrogen bonds. For chiral residues, two epimeric conformations can be distinguished, one of which is selectively formed for larger substituents at the 2‐position.