The diastereoselective formal synthesis
of (−)-quinagolide,
a D2 receptor agonist, has been achieved. The synthesis
started from l-pyroglutamic acid and relied on utilization
of (a) a stereospecific catalytic hydrogenation and diastereoselective
Horner–Emmons–Michael cascade to obtain functionalized
prolinate, (b) a Lewis acid mediated Pummerer cyclization to construct
a tricyclic fused ring system, and (c) a diastereoselective ring expansion
via a bicyclic aziridinium intermediate to access the required 3-substituted
piperidine scaffold.
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