Ketenes dichloro

Faster addition results in some polymerization of the dichloro-ketene which darkens the precipitate. 

A systematic study of the Baeyer-Villiger oxidation of cyclobutanones was recently reported by Jeffs71). The cycloalkenes (206) reacted readily with dichloro-ketene to give the gem-dichlorocyclobutanone (205), which were reduced by Zn to the cyclobutanone (204). Baeyer-Villiger oxidation of (204) yielded the y-lactone (207) in fair yields. (Table 11)71). 

Dihydroxy-4-butyrolactone, 45, 24 Diisopropylcarbodiimide, 46, 98 Diketene, pyrolysis to ketene, 46, SO -Dimethylaminobenzaldehyde, conversion to 3,g-dichloro- -dimethyl-aminostyrene, 46, 34... 

The inverse-electron-demand Diels-Alder reaction of 3,6-dichloro[l,2,4,5]tetrazine with alkenes and alkynes provides the synthesis of highly functionalized pyridazines. ° Also, the 4 + 2-cycloaddition reactions of the parent [l,2,4,5]tetrazine with donor-substituted alkynes, alkenes, donor-substituted and unsubstituted cycloalkenes, ketene acetals, and aminals have been investigated. ... 

Ketene itself and simple alkylketenes are inert towards nonactivated alkenes. F or the preparation of cyclobutanones formally derived from ketene or an alkylketene and nonactivated alkenes, the more reactive dichloroketene or alkylchloroketenes can be used. The corresponding a,a-dichloro- or oc-chlorocyclobutanones can readily be dechlorinated by treatment with zinc in acetic acid, or tributyltin hydride in near quantitative yields. F or example cycloaddition of substituted cyclohexene to dichloroketene gave dichlorocyclobutanone 1 which was dechlorinated to 2 with zinc.13,18 Likewise cycloaddition of cycloalkcnes to chloro(methyl)ketene gave 3 which was dechlorinated to 4.14... 

Chloroacetic Acid (ClCHiCOOHf. [CAS 79-11-8 J. Chloroacelic acid can be synthesized by the radical chlorination of acetic acid, treatment of trichloroethylene with concentrated H S04. oxidation of 1.2-dichloro ethane or chloroaceialdehyde. amine displacement from glycine, or chlorination of ketene. It behaves as a very strong monobasic acid and is used as a strong acid catalyst for diverse reactions. The Cl function can be displaced in base-catalyzed reactions. For example, it condenses with alkoxides to yield alkoxyacetic acids CICH COOH... 

The production of buta-1,3-dienes (37) by reaction of 1,2-diarylcyclopropenes with dihalocarbenes is thought to involve electrophilic attack of the carbene to give a dipolar intermediate (38).51 The addition of carbene to CO and H2C=0 has been studied by MNDO calculations.52 Photolysis of diethyl diazomalonate in a CO matrix at low temperature gave rise to ketenes by immediate trapping of the postulated carbene (39).53 The major products of reaction between dichlorocarbene and cyclone were CO and the gem-dichloro species (40).54 The predominance of this pathway over formation of the dichlorooxirane or the cyclopropane is attributed to the aromatic nature of the carbonyl ylide and its twist geometry. 

Mulzer et al. have extended the applicability of the insertion reaction of ketene into an acetal, to that of a substituted ketene into a 1,3-dioxalane to provide an elegant synthesis of 6,6-dichloro-l,4-dioxepan-5-ones (Equation 13) <1996AGE1970>. 

The (2 + 2) cycloaddition reactions of ketenes with alkenes are synthetically useful routes to cyclobutanones. Ketenes are particularly useful due to the low steric hindrance at the carbonyl carbon. An example is the reaction of dichloro-ketene with cyclopentadiene which, after reductive dechlorination of the product, gives bicyclo[3.2.0]hept-2-en-6-one (Expt 7.25). 

DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone) conveniently oxidizes ketene silyl acetal (15) to give a-alkoxycarbonyl iminium salt (16)63 Subsequent reaction with nucleophiles gives amino ester derivatives, Nu-CH(NBn2)-C02R. Grignards... 

Aceto(carbonyl)cyclopentadienyl(tri-phenylphosphine)iron. 3-Acylthiazolidine-2-thiones. Bis(cyclopentadienyl)titana-cyclobutanes. Bromomagnesium diisopro-pylamide. Cerium(III) chloride. Dichloro-phenylborane. Dimethylphenylsilyllithium. Ethylene chloroboronate. Ketene bis(trimethylsilyl)ketals. Mandelic acid. Norephedrine. Potassium fluoride-Alumina. (S)-(—)-Proline. Tetra-n-butylam-monium fluoride. Tin(IV) chloride. Tin(II) trifluoromethanesulfonate. Titanium(IV) chloride. Tri-n-butyltin fluoride. Trityl perchlorate. 

Similarly, the quinidine-catalyzed cycloaddition of ketene to 2,2-dichloro aldehydes gives -lactones of high optical purities which are easily converted to the corresponding methyl (3S)-hydroxyalkanoates (Scheme 3). °... 

Ketene acetals react with dichloro(phenyl)methane and sodium " or potassium tcrt-butox-ide " to afford l,1-dialkoxy-2-chloro-2-phenylcyclopropanes, e.g. S, " which generally enter readily into further reactions. 

A general synthesis of fused methylenecyclopropanes employs the carbenoid ring contraction of bicyclic cyclobutanone tosylhydrazones, available from [2-1-2] cycloaddition of dichloro-ketene to alkenes. ... 

Some thermally forbidden [2 + 2]-cycloaddition reactions can be promoted by Lewis acids1-6. With chirally modified Lewis acids, the opportunity for application in asymmetric synthesis of chiral cyclobutanes arises (for a detailed description of these methods see Sections D.l. 6.1.3.. D.l. 61.4. and references 7, 28-30). Thus, a chiral titanium reagent, generated in situ from dichloro(diisopropoxy)titanium and a chiral diol 3, derived from tartaric acid, catalyzes the [2 + 2]-cycloaddition reaction of 2-oxazolidinone derivatives of a,/ -unsalurated acids 1 and the ketene thioacetal 2 in the presence of molecular sieves 4 A with up to 96 % yield and 98% ee. Fumaric acid substrates give higher yields and enantiomeric excesses than acrylic acid derivatives8. Michael additions are almost completely suppressed under these reaction... 

---