Donorsubstituierte Benzenderivate als Dienophile in der [4 + 2]-Cycloaddition mit inversem Elektronenbedarf

✍ Scribed by Hoferichter, Reinhard ;Seitz, Gunther

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 564 KB
• Volume: 1992
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1992199201189

✦ Synopsis

Donor‐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.