Bicyclo octanes, enamines

In an approach to the AB rings of rubrolone 65, Boger examined the use of oxazinones as a replacement for triazines. Reaction of l,3-oxazin-6-one 66 with enamines 67 produced the corresponding pyridines 70. The reaction proceeds in a manner analogous to the triazines however, instead of losing nitrogen, these systems lose CO2 via the intermediate bicyclo[2.2.2]octanes 68. The resultant 69 then loses pyrrolidine as in the triazine example. 

The potential of Fischer carbene complexes in the construction of complex structures from simple starting materials is nicely reflected in the next example. Thus, the reaction of alkenylcarbene complexes of chromium and tungsten with cyclopentanone and cyclohexanone enamines allows the di-astereo- and enantioselective synthesis of functionalised bicyclo[3.2.1]octane and bicyclo[3.3.1]nonane derivatives [12] (Scheme 44). The mechanism of this transformation is initiated by a 1,4-addition of the C -enamine to the alkenylcarbene complex. Further 1,2-addition of the of the newly formed enamine to the carbene carbon leads to a metalate intermediate which can... 

Whitney JG, Gregory WA, Kauer JC, Roland JR, Snyder JA, Benson RE, Hermann EC (1970) Antiviral agents. I. Bicyclo[2.2.2]octan- and -oct-2-enamines. J Med Chem 13 254-260... 

An unusual ring-chain tautomerism in bicyclo[4.2.0]octane derivatives 7 has heen reported [19]. The reversible transformation of the cyclobutane derivative into a tris-substituted enamine was studied by NMR spectroscopy (Scheme 5.5). 

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