Selective derivatisation of resorcarenes, 6 - Mannich reactions with aminoalcohols

The condensation of resorcarenes 1 with various amino alcohols and an exces s 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, a nd 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 w ith alkyl groups, the tetraoxazolidines 4 are the preferred reaction produc ts, while 1-methyl aminoethanol (1-amino-propan-2-ol) yields predominantly the tetrabenzoxazine 2f. The structures of all these compounds have been co nfirmed by NMR spectroscopy and additionally by single-crystal X-ray analys is 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, wh ile the equilibrium is shifted to the less polar tetraoxazine or tetraoxazo lidine in CDCl3. Low-temperature NMR spectra show a C-4-symmetrical conform ation for the tetraoxazolidines 4 in CDCl3 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 a t the 2-position.