Benzocyclobutene derivative

Analogous reactions were used for the preparation of various benzocyclobutene derivatives [13-15],... 

Heating of the benzocyclobutene derivative 1 in degassed o-dichlorobenzene at 180°C for 2 hours gives the spirocyclic product 2 in 88% yield. 

A significant acceleration of the electrocyclic ring opening of benzocyclobutene derivatives has been disclosed under the influence of a -silicon atom.55 This effect has been associated with the adjacent anion-driven electrocyclic reactions such as oxy-Cope rearrangement. 

The cobalt(I)-mediated [2 + 2 + 2] cycloaddition of 1,5-diynes with mono-alkynes provides access to benzocyclobutene derivatives (Scheme 24). Thermal rearrangement of benzocyclobutenes into o-quinodimethane and subsequent Diels-Alder reaction with an alkene moiety allow the formation of a tricyclic compound. 

The next three reactions (Scheme 3.38), cotrimerization of enediyne 146 with bis(trimethylsilyl)acetylene 150, thermolysis of the benzocyclobutene derivative 151, and the intramolecular Diels-Alder reaction of the intermediate 152, were... 

A major initial limitation of the benzocyclobutene approach to o-quinodimethanes was the lack of efficient, large-scale syntheses for many specifically substituted derivatives. Fortunately, recent developments have lemov much of this impediment. Q>nceptually, the synthesis of benzocyclobutenes from aromatic precursors can be envisaged in only a limited number of ways. These include [2 -i- 2] cycloadditions involving benzynes and alkenes, intramolecular cyclization on to a benzyne, cyclizations involving arene anions, and electrocyclic closure of o-quinodimethanes. Benzocyclobutene derivatives can also be prepared by aromatization of bicyclo[4.2.0]octanes. Detailed discussion of variations to these approaches can be found in the cited reviews. The cobalt catalyzed co-oligomerization of 1,5-hexadiynes with al-kynes, especially bis(trimethylsilyl)acetylene, has also been employed for the preparation of specifically substituted benzocyclobutenes. In the latter case the cyclobutenes are often not isolated but converted directly to o-quinodimethanes and subsequent products. ... 

Under yet another. set of conditions ([Pd(PPh3)4], K2CO3, DMF, 80 °C) intermediate 139, which is common to the formation of 136/137 and 138, reacts with norbornene (53) to afford the benzocyclobutene derivative 140 (Scheme 3-36) [189a]. 

An unusual C — H activation on orf/zo-methoxy groups was observed by Dyker et al., in the reaction of methoxyiodoarenes such as 144 leading elegantly to 6//-dibenzo[/ , /]pyrans such as 145 (Scheme 3-38) [190,191]. Under the same conditions, 2-rert-butyliodobenzene (146) with various aryl halides gave the benzocyclobutene derivatives 147, the formation of which also involves an alkyl C — H activation [190e]. 

II. The benzocyclobutene derivative can be prepared by direct reaction of o-bromobenzyl bromide with RgSiCla in the presence of magnesium 108, 129). The small membered ring system has also been synthesized by ring closure with formation of one ring bond ... 

In contrast to 69, the all-ct s and mono-trans thionins 70 and 71 are non-planar and have to be viewed as dimethylene benzocyclobutene derivatives of presumably insignificant cyclobutadienoid character88. ... 

The first example of an intramolecular imino Diels-Alder reaction was described by Oppolzer, who found that on heating a benzocyclobutene derivative a mixture of epimeric tricyclic adducts was formed [Eq. (231].80... 

Benzocyclobutene derivatives have also been used to alkylate a bicyclo[2.2.1] heptane which after transformation to the appropriate vinyl derivative has been thermolysed to yield the the tetracyclic structure of estradiol methyl ether (ref. 126) which latter upon oxidation with Jones reagent and demethylation ot the... 

A number of di- or trimerization reactions of aryl and vinyl halides, which are mechanistically related to those in Eqs. 37 and 38 [7], have been reported. Interestingly, in the reaction of o-tert-butyliodobenzene,one of the aliphatic C-H bonds in the ortho substituent is intramolecularly activated and the successive reaction with another iodide molecule leads to a benzocyclobutene derivative (Eq. 41) [112]. A monomeric benzocyclobutene is produced selectively in the case of ethyl 2-(2-bromophenyl)-2-methylpropionate (Eq. 42) [113]. 2-(2-Bro-mophenyl)-2-ethylbutanoate undergoes an intramolecular redox reaction, that is, dehydrobromination-unsaturation (Eq. 43). The reaction has been proposed to proceed via C-H bond activation at one of the terminal methyl groups and P-hydrogen elimination. 

The benzocyclobutene derivative 141 was prepared as previously described. The AB ring system was synthesized from l-cyano-4-methoxyben-zocyclobutene by heating with an excess of isoprene (180°, 2 hours), yielding a mixture of isopropenyl and vinyl methyl tetralins 145 and 146, respectively (Scheme 21). The desired material 145 was obtained by chromatography in 43%... 

Cases exist, such as the natural or commercial preparation of provitamin D from provitamin D (Sect. 1) or the ring opening of cycIohexa-2,4-dienones to their dieneketene seco-isomers (Sect. 2), in which the photoreaction has the advantage. There are other instances such as the preparation of reactive or//(o-quinodimethane derivatives as intermediates in steroid synthesis ) (Sect. 3), in which either pliotoenoKzation or thermal seco-isomeriza-tions of appropriate benzocyclobutene derivatives may be used equally weU. 

PROPERTIES OF SPECIAL INTEREST BMI resins are generally brittle. They can be toughened with additives such aromatic diamines (chain extension via Michael Addition reaction), divinylbenzene or bis (ally Iphenyl) compounds (chain extension via Diels-Alder reaction and ene reaction, respectively), benzocyclobutene derivatives (chain extension via Diels-Alder reaction), low molecular weight rubber, and thermoplastics. Certain bismaleimides are liquid crystalline. ... 

The Parylene family has very attractive properties for use as dielectric materials as was noted above, but their thermal stability at the temperatures used in the fabrication of electronic devices is less than optimum. When considering alternatives as possible precursors for VDP, the isomeric ortho-xylylene (o-quinodimethane) is a likely candidate (Scheme 4). This approach involves the thermolysis of benzocyclobutene derivatives to generate a reactive dieneoid intermediate (o-quinodimethane),... 

DeVries, R.A., Vosejpka, PC. and Ash, M.L. (1998) Homogeneous palladium catalysed vinylic coupling of aryl bromides used to make benzocyclobutene derivatives. Chem. Ind., 75,467-78. 

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