Benzocyclobutene nitrile

Barbituric acid, 191 Benzisoxazole, 240, 242-243 Benzocyclobutane, 114 Benzocyclobutene nitrile, 149-150... 

Cyclization of side chain nitriles has found extensive use in the synthesis of benzocyclobutenes (70 n = 2),104 the versatile synthons which open on mild thermolysis to give o-quinodimethanes for inter- and intra-molecular [4 + 2] trapping.108 The nitrile group in (70) can be manipulated into a variety of functionalities for appending the dienophile portion. For example, in the synthesis of chelidonine, the nitrile (71) was converted, by hydrolysis followed by Curtius degradation and reaction of the formed isocyanate with benzyl alcohol, to a urethane (72). The latter was then condensed with a benzyl bromide to get the compound (73), which was elaborated further as shown in Scheme 14.109... 

The influence of intramolecularity on the benzocyclobutene-fulvene cycloaddition was illustrated in dramatic fashion when the two reactive units were tethered together by a three-carbon chain. Heating nitrile (58) gave only the [6 -1- 4] cycloadduct (59) as an inseparable mixture of cyclopentadiene isomers in... 

An early but important example of this style of tandem reaction is based on the benzocyclobutene 148, easily prepared from the nitrile 146 by cyclisation of the benzyne19147. 

Bromine-lithium exchange in 2-(2-bromoethyl)bromobenzenes using Bu Li at low temperature gives the corresponding aryl-lithiums, which may be warmed to effect cyclization to benzocyclobutenes or treated with nitriles to give 3,4-dihydro-isoquinolines/ ... 

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