Cyclobutenes 3,4-dichloro

Fluorinated cyclobutanes and cyclobutenes are relatively easy to prepare because of the propensity of many gem-difluoroolefins to thermally cyclodimerize and cycloadd to alkenes and alkynes. Even with dienes, fluoroolefins commonly prefer to form cyclobutane rather than six-membered-ring Diels-Alder adducts. Tetrafluoroethylene, chlorotrifluoroethylene, and l,l-dichloro-2,2-difluoroethyl-ene are especially reactive in this context. Most evidence favors a stepwise diradical or, less often, a dipolar mechanism for [2+2] cycloadditions of fluoroalkenes [S5, (5], although arguments for a symmetry-allowed, concerted [2j-t-2J process persist [87], The scope, characteristic features, and mechanistic studies of fluoroolefin... 

A1( -octalone, 45, 80 N-nitioso-N-phenylglycine to N-phenylsydnone, 45, 96 Cyclobutanecarboxylic acid, reaction with hydrazoic acid, 47, 28 Cyclobutene, 1,2,3,4-tetrasiethyl-3,-4-dichloro-, 46, 34 reactions of, 46, 36 Cyclobutylamine, 47, 28 Cyclobutyl isocyanide, 46, 77 Cycloheptanone, 45, 31... 

Although the orbital-symmetry rules predict the stereochemical results in almost all cases, it is necessary to recall (p. 1070) that they only say what is allowed and what is forbidden, but the fact that a reaction is allowed does not necessarily mean that the reaction takes place, and if an allowed reaction does take place, it does not necessarily follow that a concerted pathway is involved, since other pathways of lower energy may be available.Furthermore, a forbidden reaction might still be made to go, if a method of achieving its high activation energy can be found. This was, in fact, done for the cyclobutene butadiene interconversion (cis-3,4-dichloro-cyclobutene gave the forbidden cis.cis- and rran.y, ra i -l,4-dichloro-1,3-butadienes,... 

The oxidation of 2,2-dichloro-3-cyclobuten-l-ones 241 with VO(OR)Cl2 results in the regioselective formation of alkyl 2,4,4-trichloro-3-butenoates 242 with chlorination at the a-position of 243 [140]. (Scheme 97)... 

CYCLOBUTANONE, 51, 76 CYCLOBUTANONE VIA SOLVOLYTIC CYCLIZATION, 54, 84 Cyclobutanones, 54, 32 CYCLOBUTENE, cis-3,4-DICHLORO-,... 

Dichloro-I, 2,3,4-tetramethyl-CYCLOBUTENE, 46, 34 o,a-Dichlorotoluene, condensation with ethyl cyanoacetate, 48, 54 Dicyclohexylcarbodiimide in oxidation of cholane-24-ol with dimethyl sulfoxide and pyridinium trifluor-oacetate, 47, 25... 

Dehalogenation has also been employed in the preparation of cyclobutenes. For example, stereoisomerically pure l,2-dichloro-3,4-dibromocyclobutane (18) reacts with 0.5% lithium amalgam in diethyl ether to give the nnf/ -tricyclooctadiene 32, which is isolated as its corresponding disilver(I) complex 31.11 However, similar treatment only converts tetrachlorocy-clobutane (16) to yyn-tricyclooctadiene 34 in very low yield.11... 

Retention times for the various components (minutes) are cyclobutene 2, 2.6 trans- 1,2-dicyanocyclobutane, 3.6 two isomeric l,2-dichloro-l,2-dicyanocyclobutanes, 5.1 and 5.9, respectively cis-l,2-dicyanocyclobutane, 9.8. 

Three syntheses of 1,2-dicyanocyclobutene (2) have been previously described. The first, involving dehydration of cyclobutene-1,2-dicarboxamide does not specify the yield.9 The second procedure involves a concomitant chlorination and catalytic dehydrochlorination of 1,2-dicyanocyclobutane in the gas phase, yielding 1,2-dicyanocyclobutene (2) in a mixture of several other products.10 The third method consists of dechlorination of 1,2-dichloro-1,2-dicyanocyclobutane using metals, such as zinc copper couple,11 Raney nickel,11 and, especially, Raney cobalt.2 In comparison with this last-mentioned synthesis, the overall yield of the present procedure is 5-10% higher. Furthermore, the reaction is performed in less time and utilizes considerably cheaper reagents. 

POLYHYDROGEN FLUORIDE REAGENT 1-FLUORO-ADAMANTANE. Dichloroalkane synthesis is shown in cis-DI-CHLOROALKANES FROM EPOXIDES cis-1,2-DICHLORO-CYCLOHEXANE. Nitrile functionality can be introduced from a ketone, as in NITRILES FROM KETONES CYCLOHEXANENITRILE, or from a reactive diene, as shown in 2,3-DICYANOBUTADIENE AS A REACTIVE INTERMEDIATE BY in situ GENERATION FROM 1,2-DICYANO CYCLOBUTENE 2,3-DICYANO-1,4,4a,9a -TETRAHYDRO-FLUORENE. 

Reaction of 1,2,3-trimethylcyclopropene with trichloromethyl lithium generated from bromotrichloromethane and methyl lithium at —110 °C produces the cyclobutene (279). This may be explained in terms of intermediate formation of the bicyclobutane (280), followed by cyclopropyl-allyl rearrangement, though the dichloro-cyclopropane could not be detected even at —73 °C 209). 

With CF3C=CCF3 or olefins with an internal double bond such as cis- or fraras-F-2-pentene, F-cyclobutene, or l,2-dichloro-l,2-difluoro-ethylene, or with a geminally disubstituted olefin such as 1,1-dichloro-2,2-difluoroethylene, only fully fluorinated products were obtained, likely through a nucleophilic fluorination mechanism. This fact, plus the necessity for a Lewis acid catalyst for addition to proceed, is evidence for an electrophilic addition mechanism. Others have suggested polar addition of BF3 to the olefin with RfBF2 as a reactive intermediate (294). 

Generally the best result.s are obtained when the alcoholate of a fluorinated compound reacts with a nonfluorinated alkyl halide. Yields decrease when both alcohol and halide contain fluorine. The reaction of dichloro compound 9 with alcoholates 10 to monoethers II is representative of a variety of similar transformations (which proceed via an addition/elimination mechanism) of cyclopropcne, cyclobutene.cyclopentene" or cyclohexene derivatives." ... 

Cyclobutene 4,4-Dichloro-l, 2-dipropyl-3-oxo- E17f, 960 (3,3-Cl2 — 1,2-R2—cyclopropen + CC12)... 

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