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Nickel‐Catalyzed [2+2] Cycloaddition of Alkynes with Activated Cyclic Alkenes: Synthesis and Novel Ring Expansion Studies of Cyclobutene Products
Author(s) -
Huang DawJen,
Rayabarapu Dinesh Kumar,
Li LihPing,
Sambaiah Thota,
Cheng ChienHong
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001016)6:20<3706::aid-chem3706>3.0.co;2-p
Subject(s) - cyclobutene , cycloaddition , triple bond , chemistry , ring (chemistry) , medicinal chemistry , alkyne , yield (engineering) , catalysis , toluene , double bond , organic chemistry , materials science , metallurgy
Oxabenzonorbornadienes 1 and 2 and azabenzonorbornadiene 3 undergo [2+2] cycloaddition with alkynes (PhC≡CPh, PhC≡CMe, PhC≡CCO 2 Et, PhC≡CCH(OEt) 2 , and HC≡C(CH 2 ) 4 Me) in the presence of [Ni(PPh 3 ) 2 Cl 2 ], PPh 3 , and Zn powder in toluene to afford the corresponding exo ‐cyclobutene derivatives 4 a – e, 5 a – e , and 6 in fair to excellent yields. Under similar conditions, EtCO 2 C≡CCO 2 Et does not react with 1 in toluene to give the [2+2] cycloaddition product, but in acetonitrile, the catalytic [2+2] cycloaddition proceeds and cycloadduct 4 f is isolated in 83 % yield. At high temperature, these cyclobutene derivatives readily undergo ring expansion to yield the corresponding 8‐membered carbocyclic dienes. Thus, flash vacuum pyrolysis of 4 a, 4 d, 4 f, 6 , and 14 at 500 °C affords dienes 13 a – d and 15 in 70–96 % yields. This interesting ring expansion may be viewed as the insertion of an alkyne moiety into the carbon–carbon double bond of a cyclic olefin resulting in the enlargement of the ring by two carbons. Compound 13 a is readily deoxygenated by TiCl 4 and Zn in THF to give a cyclooctatetraene derivative 16 in 89 % yield.