Benzocyclobutane derivatives

The curious reaction of benzyne with 1-pyrrolidinocyclohexene leads to a benzocyclobutane derivative in addition to a small amount of 2-phenylcycIohexanone.234... 

Enals and enones as well as ketones react with orfho-functionalized bromo-benzenes to give the corresponding cyclized products (cf. Eqs. 22-24). The reaction of o-dibromobenzenes with alkenals gives benzocyclobutane derivatives (Eq. 29) [61]. 1-Naphthol derivatives are produced by using o-bromobenzalde-... 

For example, irradiation of the anthracene endoperoxide 547 at / irr = 400 nm leads to the. svn-diepoxide 548 at low temperatures (Scheme 6.263). Upon heating, the product isomerizes to the benzocyclobutane derivative 549.1449... 

Sol 3. (i) A stereoselective total synthesis of estrone proceeds via thermal 47T-conrotatory ring opening reaction of benzocyclobutane derivative to generate reactive o-quinodimethane intermediate followed by an intramolecular Diels—Alder reaction. 

Enamides 34 have been also described as useful partners for [2+2] cycloaddition reactions with benzyne (1) to afford amido-functionalized benzocyclobutane derivatives 35. By engaging this process with a pericyclic ring-opening intramolecular [4+2] cycloaddition, the total syntheses of cheli-donine 37a and norchelidonine 37b from the corresponding aryne precnrsor and enamide 36 have been reported (Scheme 12.21) [33]. 

Aromatic compounds can participate in both [2+2] and [4+2] photocycloaddition reactions with uracil derivatives to give either benzocyclobutane or ethenoquinazoline (barrelene) derivatives, which can then undergo a number of subsequent photochemical reactions. The products obtained are dependent upon the reaction conditions, and thus the photocycloaddition reaction between naphthalenes 470 and l,3-dimethyl-5-fluorouracil 471 in cyclohexane gave 4a-fluoro-5,10-ethenobenzo[/]quinazolines 472 as products as a result of a [4+2] photocycloaddition (photo-Diels-Alder) reaction <2002TL3113, 2003H(61)377>. 

Diazetidines. A saturated four-membered ring containing two adjacent nitrogen atoms is named a 1,2-diazetidine 1. When the two nitrogen atoms and the two carbon atoms are alternatively present in the four-membered ring, it is named a 1,3-diazetidine 2, which is also known as uretidine. Fused multinuclear heterocyclic systems are known as diazacyclobutane derivatives. For example, 3,4-benzo-l,2-diazetidine is referred to as l,2-diaza-3,4-benzocyclobutane 3. 

Steroids.—Intramolecular Diels-Alder reactions of o-quinodimethanes, generated by thermolysis of the corresponding benzocyclobutanes, continue to form the basis of many steroid syntheses, " including estradiol derivatives, 18-hydroxyestrone, (+)-chenodeoxycholic acid, and des-A-ring steroids. Two alternative ways to obtain o-quinodimethanes, by photoenolization of o-methylphenyl ketones or by a fluoride-ion-induced elimination reaction [(191)- (192)1, have been utilized in syntheses of 19-nor-steroids and O-methyl estrone (193), respectively. 

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