Imines strained bridgehead

The formation of highly strained bridgehead imines was observed on the irradiation of a series of matrix-isolated bridgehead azides.The photochemistry of matrix-isolated 1-azidonorbornane (6) was studied using monochromatic irradiation IR, UV, and ESR spectroscopy and trapping with methanol and CO. The azide photochemistry was very complicated, and the formation of two types of imines (7 and 8) and triplet nitrene 9 were observed. 

New highly strained bridgehead imines, aza-analogu of adamantene, have been reported. ... 

Surprisingly, imino carbon shifts of strained 2 7/-azirines [431] do not differ substantially from those of open-chain imines (Section 4.9.3). On the other hand, the alkene carbon shifts of l-azabicyclo[2.2.2]oct-2-ene do not reflect the polarization characteristic of other enamines (Section 4.9.2) (+ )-M electron donation of the bridgehead enamino nitrogen cannot take place since the lone-pair orbital and the p orbitals of the it bond are... 

Simultaneously, Woodward and co-workers (21) confirmed structure X for the alkaloid by chemical methods. They first recorded the caly-canine synthesis already mentioned. The intermediate tetraaminodi-aldehyde, first postulated by Robinson and Teuber (10), was also the basis for their structural speculations. The mercuric acetate oxidation product (dehydrocalycanthine) of Marion and Manske (13), formed by loss of two hydrogens, was smoothly converted by the action of alcoholic alkali into methylamine, and the resulting amide alcohol was written as XI. It was concluded that dehydrocalycanthine is an ene-imine, the relevant portion of the molecule being shown as XII. Other structures derivable from the tetraaminodialdehyde would more probably generate on amidine, and this would be impossible with X because of steric strain at a bridgehead double bond. 

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