Endo isomers, definition

B-adducts involve the -carbon atom endo/exo notation, as usual, defines the di-astereoisomeric relation of the C-N-0 nitrone-group with respect to the substi-tuent(s). The isomer definition is made clearer in the transition structures which are taken to be "concerted according to the extant literature. One can see that all the adducts allowed are present in the reaction mixture with variable, but non negligible fractions. The same is true for the reactions of 3,4-dihydro-isoquinoline-N-oxide and C-phenyl-N-methylnitrone,3 whereas the reactions of N-H-nitrone (H-nitrone), N-Me-nitrone and N-(t)-Bu-nitrone3t>.c lead to a single adduct, which, in our notation, is the B-regioadduct (Scheme 3). The experimental trends extracted from Tables 1-2 and from the cited literature can be summarised as follows ... 

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