4-Acyl-2,3,4,5-tetrahydro-2-methyl-2,5-methanobenz-1,4-oxazepine, Derivatives of a New Heterocycle

✍ Scribed by Dr. Hans-Joachim Kabbe; Dr. Helmut Heitzer; Dr. Liborius Born

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 336 KB
• Volume: 30
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.199117091

✦ Synopsis

highly-aggregated dilithiated organics akin to 1 include the nitrile dodecamer 2[6a1 and the sulfone hexamer 3.[6bl It is also noteworthy that the core of 1 can be considered as belonging to the fluorite (CaF,) structural type (N corresponding to Ca, Li to F ) and that even the "external" Et,O-complexed Li atoms fit this quasi-isomorphicity. Many AB, species, including alkali metal oxides and sulf i d e ~~~" ' (and, indeed, Li,NH[7b1), crystallize in this fluorite arrangement.

An unexpected feature of 1 is that it is paramagnetic. The ' H N M R signals found for 1 in benzene solutions are broad. The 7Li N M R spectrum (139.97 MHz) of 1 in the same solvent at 25 "C shows (most unusually) three distinct resonances. centered at 6 = 3.34, 0.69, and -1.35 (the reference is PhLi in benzene); however, these signals are too broad to allow meaningful integration. The repeated ESR spectra of solid 1 (in a sealed tube under an inert atmosphere) measured between 4.5 K and room temperature consist of a single, slightly asymmetric signal, which can not be attributed to common impurities such as iron or oxygen. No hyperfine interaction could be resolved, though broadening in the shoulders of the signal may be associated with a nitrogen hyperfine interaction (if so, the nitrogen coupling constant would be ca. 15 G). The resonance has a g value of 2.0047 & 0.0005 and a line width AHpp = 17 G f 0.5 G and remains essentially unchanged at all temperatures. The g value is consistent with that of a low symmetry nitrogen radical with a p5 Configuration, though a neutral (1-C,oH,NLi,),o cluster requires all ten nitrogens to have p6 configuration. Since we observed no signal attributable to a naphthyl radical anion, charge transfer from N to the naph-thy1 unit seems unlikely. At this stage we cannot deduce the number of unpaired electrons in the cluster.

The structure of 1 can be understood in terms of electrostatic bonding between Li+ cations and organic anions. A