Benzocyclobutene, 3-methyl

A similar synthesis starts from commercially available 1,5-hexadiyne and 2-methyl-cyclopent-2-enone. The benzocyclobutene is obtained from a bis-acetylene in a cobalt-catalyzed reaction. It rearranges regio- and stereoselectively to a 3-deoxy steroid derivative. The overall yield from the cyclopentenone was 40% (R.L. Funk, 1977). 

For the synthesis of estradiol methyl ether 4-319, the cydobutene derivative 4-317 was heated to give the orthoquinonedimethane 4-318 which cydized in an intramolecular Diels-Alder reaction [109]. The thermally permitted, conrotatory elec-trocyclic ring-opening of benzocyclobutenes [110] with subsequent intramolecular cycloaddition also allowed the formation of numerous complex frameworks (Scheme 4.70). 

Photolysis of a mesitylsilene (24, R=mesityl) led to insertion into one of the methyl C—H bonds yielding a benzocyclobutene (209) insertion of silenes into C—H bonds is not a very common reaction of silenes. 

In the reaction of nucleogenic atoms with toluene, the methyl group traps an initially formed o-tolylcarbene (54) as benzocyclobutene (55). A partial degradation of 55 and an examination of the label distribution indicated that 43% of 55 arose from 54 formed by an initial C—H insertion (Eq. 34). The remainder of the label in 55 was in the ring, indicating the initial formation of the m- and p-tolylcar-benes and/or a methylcycloheptatetraene. 

Perfluorostyrene analogs can be isolated from perfluoro(3-ethyl- and perfluoro(3-isopropyl-1,2-benzocyclobutene), as well as from perfluoro(3,3-dialkyl-l,2-benzocyclobutenes).29-31 For example, perfluoro(3-ethyl-3-methyl-l,2-benzocyclobutene) (36) can be converted into an EjZ mixture of the perfluorostyrene 37 at 50 CC in 91 % yield.30 Heating 37 at 130CC in the presence of antimony(V) fluoride gives the corresponding indane 38. The mechanism of these reactions has been discussed in a review article.32... 

The ratio of benzocyclobutenes formed from A and B is 1 9 (yield 50% at 83% conversion). The reaction proceeds similarly with 3-((3-methylbut-3-enyl)oxy)phenol (ratio 1 5) and with 3-(pcnt-4-cnyloxy)phenol (ratio 1 2), but it fails with 3-(hex-5-enyloxy)phenol. Understandably, when there is a 2-methyl group on the arene, the product from A is not formed. 

We can now let you into the secret of that chemical reaction . A benzocyclobutene was heated with methyl acrylate to give a 1 1 mixture of the two isomers. What is the mechanism of the reaction and why is only one regioisomer but a mixture of stereoisomers formed Isomer B is converted into isomer A on treatment with base. What is the stereochemistry of A and B ... 

Benzocyclobutene l,2-Bis-[methyl-iminoj-tetrachloro- E17f, 1031 (Cl8-4,5-H2-benzocycIobuta-diene + R —NH2)... 

Benzocyclobuten 1 -Hydroxy-2-methoxy-1 -methyl-El7f, 636/667 (2-Acyl-Ar-CH2 —OR/hv)... 

Benzocyclobuten 4,5-Bis-[methoxy-methyl]- E17f, 651 (1,5-Diin 4- In) lH,4H-(Benzo d -l,2-dioxin), ... 

Acetopbenon 4-(2-Trimethylsilyl-ethyl)- VII/2a, 61 Benzocyclobuten 5-(Methoxy-methyl)-4-trimethylsilyl- E17f, 651 (1,5-Diin + In)... 

Stevens and Bisacchi have carefully examined the trailing of benzynes, generated fiom a number of aryl bromides and sodium amide in THF, with 1,1-dimethylethylene and report procedures which afford 6 6% yields of 1,1-dimethoxycyclobutenes, e.g. (131). These compounds are hydrolyzed quantitatively to the corresponding benzocyclobutenones (132). Excellent regioselectivity was obtained with unsym-metrical benzynes derived from methoxy substituted bromobenzenes due to the polarized nature of the benzyne intermediate. Steric effects also influence regioselectivity o-bromotoluene afforded a 3 1 mixture of 3-methyl- and 6-methyl-benzocyclobutene. 

A recent study by Ward on the photolysis of o-xylene in the vacuum ultraviolet (1600-2100 A) and at 2537 A has confirmed the observations of Wilzbach and Kaplan. Benzene, toluene, ethylbenzene, m- and p-xylene and o- and m-ethyltoluene were found in much the same proportions. Furthermore the product distribution was not altered substantially at the short wave lengths. The dimer o,o -dimethylbibenzyl was observed. A new product which was observed only in the vacuum ultraviolet photolysis was benzocyclobutene from isotopic studies this product was shown to arise from the loss of a single hydrogen atom from each of the methyl groups of o-xylene. 

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