Group 13 systems saturated rings

Figure 9.16 Schematic structures of saturated group 13-pnictogen ring systems (only one resonance form is shown for the six-membered ring).

These two basic processes, with minor variants, cover the majority of the steps involved in classical heteroaromatic ring synthesis. We shall show below how a sequence of such simple steps leads, via a set of equilibria, to the final product, driven to completion by the formation of an aromatic stabilised system. In a few instances, displacements of halide, or other leaving groups, from saturated carbon are also involved. 

Ritterazine B (27), [< ]D 43° (CH3OH), showed the (M + H)+ ion at m/z 899.5873 in the high-resolution FAB+ve, which agreed with the pseudo-molecular formula C54H79N2O9. The eastern hemisphere of ritterazine B (27) was found to contain a saturated ring D, a 5/5 spiroketal system, and an OH group at C-12. The western hemisphere of 27 was identical to that of ritterazine A (26). 

Mathieson, a. McL. The Preferred Conformation of the Ester Group in Relation to Saturated Ring Systems. Tetrahedron Letters 1965, 4137. 

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