The Pearson retrosynthetic analysis of - -augustamine

Tandem intramolecular 1,3-anionic cycloadd ition-methylation 

In more recent times, 2-azaallyl anions have been much more conveniently generated by the transmetallation of 1-aminoalkylstannanes. Thus for the forward synthesis of (—)-augustamine, this would mean that the 2-azaallylstannane 5 would be the key intermediate needed. 

One of the primary dividends resulting from this disconnection was its exposure of a possible relationship between the target and a monosaccharide precursor. After systematic analysis, Pearson saw that the stereochemistry of 5 correlated perfectly with lactone 7. Furthermore, lactone 7 had a structure appropriate for easy synthetic elaboration into 6 since it was functionally differentiated at C(l) and C(4). It therefore appeared fully capable of being selectively modified in the manner required to obtain 5. 

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