Conformations of 1,p-Diazabicycloalkanes (Aza-Belted Piperidines)

Article abstract of DOI:10.1021/jo00299a026

Reduction of hexaalkylhydrazine dications produced from 2-methyl-1,2-diazabicyclo<2.2.2>octane (4) by alkylation with bis-halides produces diazabicyclo compounds, for which we refer to the nitrogen-containing n atom bridge as the "aza-belt" in the title.The compound having a five-atom <-(CH2)3N(Me)CH2-> belt, 13, exists with a boat piperidine ring having an outward paramidalized nitrogen (13-1), a conclusion based on comparison of observed 1H NMR vicinal coupling constants with those calculated using MM2 geometries.MM2 predicts that 13-1 is favored over otherconformations by at least 2.6 kcal/mol. 13C NMR chemical shifts suggest a gross conformational change between 13 and the six-atom belt compounds, <-(CH2)4N(Me)CH2-> (6) and <-CH2CH=CHCH2N(Me)CH2-> (10), for which MM2 predicts boat piperidine rings having inward pyramidalized nitrogens.PE and optical spectra of 6 and 13 are discussed. 16, the NH analogue of 13, undergoes unusually facile oxidation to give the aminal 1,5-diazatricyclo<6.2.1.0^5,10>undecane (19).It is concluded from 1H NMR vicinal coupling constants and the unusually high-field absorption of H(3e) and C(3) that 19 exists both its aminal and piperidine six-membered rings in chair conformations, which is also the MM2 prediction.