Donorsubstituierte Benzenderivate als Dienophile in der [4 + 2]‐Cycloaddition mit inversem Elektronenbedarf
1992; Wiley; Volume: 1992; Issue: 11 Linguagem: Inglês
10.1002/jlac.1992199201189
ISSN0170-2041
AutoresReinhard Hoferichter, G. SEITZ,
Tópico(s)Organic Chemistry Cycloaddition Reactions
ResumoDonor‐Substituted Benzenes as Dienophiles in the [4 + 2] Cycloaddition with Inverse Electron Demand [4 + 2] 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 observed 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 [4 + 2] 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[3,6‐bis(trifluoromethyl)pyridazine] ( 9 ) and the phthalazine 11 . In addition, with 24 as dienophile the azine 32 is formed in 24% yield. Its formation proceeds presumably via the reaction sequence 29→31→30→32 .
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