Chlorocyclobutane

In the case of an intramolecular Wurtz reaction less side-reactions are observed this variant is especially useful for the construction of strained carbon skeletons. For example bicyclobutane 5 has been prepared from l-bromo-3-chlorocyclobutane 4 in a yield of > 90% ... 

CHLOROCYCLOBUTANE, 51, 106 Mesitylene, cyanation, 50, 54 METHALATION OF 2-METHYLPYRIDINE DERIVATIVES ETHYL 6-METHYL-PYRIDINE-2-ACETATE, 52, 75 Metalation, directed, 53, 59 Methallyl alcohol, with phenyl-mercuric acetate to yield 2-methyl-3-phenylpropional-dehyde, 51, 17 METHALLYLBENZENE, 52, 115 7r-Methallylnickel bromide, 52, 115... 

Boron trifluoride etherate, co-catalyst, 53, 30, 32 a-Bromination, selective of aralkyl ketone, 53, 111 Bromine, with 3-chlorocyclo-butanecarboxylic acid and mercuric oxide to give 1-bromo-3-chlorocyclobutane, 51, 106... 

Bromo-3-chlorocyclobutane, with sodium to give bicyclo [1.1.0]-butane, 51, 55... 

Chlorocyclobutanecarboxylie acid, with mercuric oxide -and bromine to give 1-bromo-3-chlorocyclobutane, 51, 106... 

So for a molecule with two different asymmetric carbon atoms we will have not more than four stereoisomeric forms. Similarly other cyclic molecules show a similar stereoisomerism. However, with even-numbered rings certain molecules show only geometrical isomerism as in 1-methyl-3 -chlorocyclobutane. 

Semiempirical calculations on the Favorskii rearrangement of a-chlorocyclobutan-one to cyclopropenecarboxylic acid suggest that it proceeds via a stepwise semibenzilic acid pathway, both in solution and in vacuo, rather than by a cyclopropanone... 

The conversion of l-bromo-3-chlorocyclobutane to bicyclo-[l.l.OJbutane is described in Organic Syntheses.n... 

The conversion of 3-chlorocyclobutanecarboxylic acid to l-bromo-3-chlorocyclobutane is described in Organic Syntheses.8... 

With l-bromo-2-chlorocyclobutane there are cis and trans isomers and both substituted C s are chiral. Both geometric isomers form racemic mixtures. 

In l-bromo-3-chlorocyclobutane there are cis and trans isomers, but no enantiomers C and C are not chiral, because a plane perpendicular to the ring bisects them and their four substituents. The sequence of atoms is identical going around the ring clockwise or counterclockwise from C to C. ... 

The preferred reagent for Hunsdiecker-type reactions is lead(IV) acetate in the presence of an inorganic halide.18,19 The yields are usually good to excellent. Reaction of cyclobutanecar-boxylic acid with lead(IV) acetate in the presence of lithium chloride gave chlorocyclobutane (1) in good yield.18 Other carboxylic acids reacted under similar conditions.18 However, care should always be taken when lead(IV) acetate is used, as the use of this reagent in the absence of the halide results in decarboxylative elimination to give an alkene, which is found as a byproduct.19... 

A practical synthesis of bicyclo[1.1.0]butane-l-carbonitrile (67) from 3-chlorocyclobutane-l-carbonitrile by treatment with potassium Ze/7-butoxide in ttvh-butyl alcohol has been reported.25 Detailed mechanistic studies have also been carried out on the elimination of hydrogen chloride from bww-3-chlorocyclobutane-l-carbonitrile (66) and cis-3-chlorocyclobutane-l-carbonitrile (68), yielding 67.26 28 It has been reported that the elimination reactions of the two isomers are likely to proceed via a common carbanion intermediate. However, in the presence of a crown ether, the carbanion intermediates derived from the trans-isomer 66 and the ds-isomer 68 are found experimentally not to be identical. These intriguing results are attributed to the presence or absence of the potassium cation in assisting the expulsion of the leaving chloride ion.26... 

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