Nitrogen substituents, endocyclic

Fig. 4 Mechanisms of epimerization of cyclic phosphorochloridate [33a]. Several modifications of mechanisms A, C and D exist, since (i) the order of recyclization and retention steps may be switched and (ii) initial attack may be apical to endocyclic nitrogen or endocyclic oxygen if apical potentialities are similar (Hail and Inch, 1981). Ring substituents are omitted for clarity.

Several simple derivatives of azetine are known, although most of these bear substituents that help stabilize the compound by extending the conjugation of the endocyclic double bond. For example, 2-phenylazetine is obtained by the thermolysis of 1-azido-l-phenylcyclopropane nitrogen is lost from the azide group and a nitrene may be formed, prior to ring expansion (Scheme 8.2). 

There are numerous examples of the use of cyclophosphazenes with exocyclic dialkylamino or alkyl/aryloxy substituents on phosphorus as scaffolds for the formation of metal complexes. However, the number of complexes in which the endocyclic nitrogen atoms are involved in adduct formation with electrophilic... 

The first step of the mechanism is the coordination of BFI3 (Lewis acid) to the tertiary nitrogen atom (Lewis base) of the CBS catalyst from the -face. This coordination enhances the Lewis acidity of the endocyclic boron atom and activates the BH3 to become a strong hydride donor. The CBS catalyst-borane complex then binds to the ketone at the sterically more accessible lone pair (the lone pair closer to the smaller substituent) via the endocyclic boron atom. At this point the ketone and the coordinated borane in the vicinal position are cis to each other and the unfavorable steric interactions between the ketone and the CBS catalyst are minimal. The face-selective hydride transfer takes... 

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