Twelve- membered macrocyclic ring

The cyclobutane rings of 1,2-ethano[2.n]cyclophanes can be opened in a Birch reduction at — 60°C in tetrahydrofuran and liquid ammonia to give [4.n]cyclophanes.212-214 In this manner, macrocyclic rings with twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen and twenty-seven members have been synthesized. 

An alternative procedure, starting with the enamine VIII/168, gave the twelve-membered oxolactone VIII/171 via VIII/169 and VIII/170 in a yield of 4% (from VIII/168, Scheme VIII/31), [97]. Syntheses of macrocyclic lactones with an annelated aromatic ring are described by various authors. Oxidations of compounds of type VIII/172 have been investigated in order to prepare aromatic oxolactones of type VIII/173, [99], Scheme VIII/3210). 

Dioxaphosphorinans and 1,3,2-dioxaphospholans are known to dimerize to twelve- and ten-membered rings, respectively, and now 1,3,2-dithiaphosphorinans have been shown to behave in a similar way. Both dimers and monomer have been shown to interconvert when heated in an n.m.r. tube. The isolation of (103) provides a route to a variety of macrocyclic compounds analogous to (104). Attempts to pre-... 

---