molecules Review Review IndolizinesIndolizines andand TheirTheir Hetero/BenzoHetero/Benzo DerivativesDerivatives inin ReactionsReactions ofof [8+2][8+2] Cycloaddition EugeneEugene V.V. BabaevBabaev1,2,3, 1,2,3,** andand Ivan Ivan A. A.Shadrin Shadrin 1 1 11 ChemistryChemistry Department, Department, Moscow Moscow State State University, University, Leninskie Leninskie gory, Gory, 1 1 str.3, Str. 3, 119899 119899 Moscow, Moscow, Russia; Russia;
[email protected]@gmail.com 22 HigherHigher School School of of Economics, Economics, National National Research Research University, University, 7 7 Vavilova Vavilova Str., 117312 Moscow, RussiaRussia 33 N.N. D. D. Zelinsky Zelinsky Institute Institute of of Or Organicganic Chemistry, Chemistry, Russian Russian Academy Academy of of Sciences, Sciences, 47 Leninsky Ave., 119991119991 Moscow, Moscow, Russia Russia ** Correspondence:Correspondence:
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[email protected]; Tel.: Tel.: +7-985-997-94-75 +7-985-997-94-75 Abstract: PeculiaritiesPeculiarities ofof [8+2][8+2] cycloaddition of acetylenesacetylenes toto indolizinesindolizines areare reviewed.reviewed. EspeciallyEspecially mentioned are are indolizines indolizines with with leaving leaving groups groups at positions at positions 3 and 3 and 5. Cycloaddition 5. Cycloaddition to aza- to and aza- benzo and benzoderivatives derivatives are reviewed, are reviewed, as well as 1,10-cyclizations well as 1,10-cyclizations and processe ands processes leading to leading cyclazines to cyclazines where in- wheredolizines indolizines are intermediates. are intermediates. Mechanistic Mechanistic features features(adducts (adducts and cycloadducts) and cycloadducts) and theoretical and theoretical aspects aspects(one- or (one- two-steps or two-steps mechanism) mechanism) are reviewed. are reviewed. Keywords: indolizine; azaindolizines; benzoindolizines;benzoindolizines; cyclazine; [8+2] cycloaddition; mechanism; 1,10-cyclizations;1,10-cyclizations; catalystscatalysts 1.