Cyclobutanes difluoro

Fluorinated allenes are especially reactive in cycloadditions because of their highly strained double bonds [118, 119] 1,1-Difluoro- and 1-fluoroallene readily undergo both [2+2] and [4+2] cycloadditions [118 124] (equations 50-52) Exten sive studies of stereochemistry and regioselectivity show that cyclobutane forma-... 

With l,l-difluoro-2,2-dichloroethylene, butadiene yielded cyclobutane (31) in the presence of benzophenone ... 

New Cyclobutane, Cyclobutene and Cyclobutanone Derivatives derived from the Adduct of Phenylacetylene with l.l-Difluoro-2.2-dichloroethyle-ne. J. Amer. chem. Soc. 75, 4765 (1953)-... 

Difluoroallene cycloadditions occur via 1,4-diradical intermediates and are generally nonregioselective.4 This is seen in the production of both l,l-difluoro-2-methy cnecyclobutanes and (difluoromethylenc)cyclobutanes as major products in the cycloadditions of 1,1-difluoroal-iene with alkenes.14- The same is true for fluoroallcne cycloadditions except that additional isomers can occur due to EjZ isomerization of the (fluoromethylene)cyclobutanes.17... 

In certain polyfluorinated cyclic compounds difiuoromethylene groups are hydrolyzed to carbonyl groups relatively easily.141 This is usually associated with the formation of cycloalkene intermediates, since the proximity of a C = C bond notably increases the reactivity of a difluoro-methylene group towards hydrolytic reactions. Thus, easy conversion of such groups to oxo groups has been observed in many cyclobutene derivatives. 2-Chloro-l,l,2-trifluoro-3-phenyl-cyclobutane is converted by potassium hydroxide into cyclobutene 1 and cyclobut-2-enone 2.141... 

In the case of the fluorinated ethylenes, it is known through work of Bartlett and his collaborators that the reaction is stepwise by way of a biradical intermediate.17 Much of the evidence supporting this conclusion has been obtained from the study of additions of l,l-difluoro-2,2-dichloroethylene, abbreviated 1122, to dienes. Scheme 1 outlines six possible general routes, each of which has several potential stereochemical variations, that addition of an olefin to a diene could follow. When 1122 reacts with butadiene and simple substituted butadienes, the products are entirely cyclobutanes consequently, we may restrict attention... 

Diphenylallene affords a dimer characterized as 1-diphenylmethyl-ene-2-methylene-3,3-diphenylcyclobutane 18>. 1, l-Difluoro-3,3-bis (triflu-oromethyl)allene gives at 90 °C a mixture of at least seven compounds thought to be dimers and trimers 1 L). 1,1-Difluoroallene dimerizes to both the 3,3,4,4-tetrafluoro and l-difluoromethylene-2-methylene-3,3-difluoro-cyclobutane Z6>. Perfluoro-l,2-pentadiene reacts at 20 °C to produce three dimers, including 22% of a l,2-bis(difluoromethylene)cyclobutane and 63% of a l-fluoroperfluoroethylmethylene-2-difluoromethylene cycloadduct 10>. l,l-Dichloro-3,3-dimethylallene gives a mixture of dimers 25>. 

Scheme 6.49. A representation of the radicals that might be involved in the reaction of 1,1-dichloro-2,2-difluoroethene with ( )- ,3-pentadiene. The justification (in part) for suggesting that the reaction involves radicals is the observation that the product is 2,2-dichloro-l,l-difluoro-3-[l-(i )-propenyl]cyclobutane rather than the isomeric l,l-dichlor-2,2-difluoro-3-[ -( ) -propenyl] cyclobutane.

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