Generation of a stable spiro dihydroaromatic anion

Nucleophilic eliminative ring fission

“…The more stable primary ion is formed and fission of the spirocarbocyclic ring does not occur when it is five membered and only mildly strained. 39 Stabilization of the leaving group is important in poorly activated systems, and the effect is also seen below in numerous instances. Treatment of the salt 20 with sodamide in ammonia gives40 the rearranged alkene 22, probably via the intermediate cyclopropane 21 which cleaves to give a benzylic carbanion: Pr'Li Ph 14 SH Benzylic carbanions as leaving groups are also seen in rearrangement of the cyclohexadienyl anion 2341 and in 24.…”

Cyclization of Lithiated Pyridine and Quinoline Carboxamides: Synthesis of Partially Saturated Pyrrolopyridines and Spirocyclic β-Lactams

“…Thus, treatment of 6 with LDA at −40 °C and addition of methyl chloroformate led to the formation of a dearomatized product 18a in 91% yield. Instead of the 6,5-fused bicycle formed from 1 , however, 18a was a 2,7-diazaspiro[3,5]nonane, a spiro-linked β-lactam-dihydropyridine . Other acylating agents, namely, benzyl chloroformate and benzoyl chloride, were equally effective at promoting this new type of cyclization (giving 18b , c ), as was methyl triflate (which gave 18d ).…”