100330-23-2Relevant academic research and scientific papers
Donor-Substituted Benzenes as Dienophiles in the Cycloaddition with Inverse Electron Demand
Hoferichter, Reinhard,Seitz, Gunther
, p. 1153 - 1158 (2007/10/02)
Cycloadditions of various donor-substituted benzenes (2a, 2b, 12, 15, 21 and 24) with 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine (1), are described. 1 exhibits the highest diene reactivity so far abserved in Diels-Alder reactions with inverse electron demand.The unusual reactivity is in accord with frontier orbital theory; for instance with 2a, 2b and 24 cycloaddition takes place with high site selectivity in 3,4- and 1,2-position of the donor-substituted benzenes, resulting in preferential formation of the 6-substituted phthalazines 5a, 5b and 28, respectively.Main side products are in each case the (E)-4,4'-Ethylenebis (9) and the phthalazine 11.In addition, with 24 as dienophile the azine 32 is formed in 24percent yield.Its formation proceeds presumably via the reactions sequence 29 -> 31 -> 30 -> 32. Key Words: 1,2,4,5-Tetrazines / Benzenes, donor-substituted / Cycloadditions, inverse / Phthalazines
