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17.7.4 Product Subclass 4: [3.3.3]Cyclazines (Pyrido[2,1,6-de]quinolizines) and Related Compounds

DOI: 10.1055/sos-SD-017-01619

Tominaga, Y.Science of Synthesis, (2004171057.

[3.3.3]Cyclazine (pyrido[2,1,6-de]quinolizine) is of considerable theoretical interest, given that it is isoelectronic with the phenalenide anion and is formally related to [12]annulene.[‌73‌] In 1969, the synthesis of [3.3.3]cyclazine (4) was achieved by Farquhar and Leaver after a series of unsuccessful attempts by various groups.[‌130‌,‌131‌] Cyclazine 4 was found to be highly reactive, exhibiting a strong paratropic shift in the 1H NMR signals, and a high propensity toward both oxidation and reduction. This parent cyclazine 4 is air sensitive and is oxidized by halogens to a stable radical cation and to a dication 124.[‌131‌] Such properties are characteristic of compounds with a small energy-gap between the frontier orbitals. The cyclopenta[cd]cyclazine 125 is definitely diatropic, because of participation of the lone pair of the central nitrogen in the formation of a peripheral 14π-annulenic anion (Scheme 48).[‌132‌]

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