Chloroform dichlorocarbene preparation from

Schiff base 293 with dichlorocarbene, prepared from chloroform and potassium hydroxide in situ, in the presence of benzyltriethylammonium chloride afforded 2-chloro-3-phenyl-l //-pyrimido[l, 2-a]quinolin-l-one (294), l-chloro-2-phenylimidazo[l,2-a]quinoline, and l-(l-quinolyl)-2,2-dichloro-3-phenylaziridine in 5%, 8%, and 6% yields, respectively (91KGS810). 

Dihalocyclopropanes are generally prepared by the addition of dihalocarbenes to alkenic substrates. As indicated in the introduction, the first synthesis of a dihalocyclopropane was accomplished by Doering and Hoffmann by the addition of dichlorocarbene, generated from chloroform and potassium r-butoxide (Bu OK), to cyclohexene giving dichloronorcarane (1), as shown in equation (l).s... 

Dihalocarbenes, CX2, are especially useful reactive intermediates since they are readily prepared from trihalomethanes (CHX3) by reaction with a strong base. For example, treatment of chloroform, CHCI3, with KOC(CH3)3 forms dichlorocarbene, CCl2. 

Benzocyclopropene. ° Benzocyclopropene (3) can be prepared conveniently in two steps. 1,4-Cyclohexadiene (I) is treated with dichlorocarbene (generated from chloroform and potassium (-butoxide) to give 7,7-dichlorobicyclo[4.1.0]heptene-3 (2) in 41 % yield. This intermediate is then treated with potassium i-butoxide and D VTSO... 

The preparation of orthoformic acid esters from chloroform and alkali metal alkoxides is a long known procedure, " which can be performed under phase transfer catalysis. If small amounts of alcohol are present in the phase-catalyz process, cyclopropanes (372 Scheme 67) can be produced by aHHifinn of dichlorocarbene to l,2-dialkoxy-l,2-dichloroethylenes, which are thought to be intermediates. " Al-kenes of this kind, e.g. (373 equation 176), have been observed as byproducts in the synthesis of tri-r-butylorthoformate from chlorodifluoromethane or dichlorofluoromethane and potassium r-butoxide. Trimethoxyacetonitrile was prepared from trichloroacetonitrile and sodium methoxide. ... 

Dichlorocarbene is prepared from the reactions of chloroform in a strong base. 

Cyclopropanes may also be synthesized from halogenated carbenes, which are prepared from halomethanes. For example, treatment of trichloromethane (chloroform) with a strong base causes an unusual elimination reaction in which both the proton and the leaving group are removed from the same carbon. The product is dichlorocarbene, which gives cyclopropanes when generated in the presence of alkenes. 

The present method utilizes dichlorocarbene generated by the phase-transfer method of Makosza4 and Starks.5 The submitters have routinely realized yields of pure distilled isocyanides in excess of 40%.6 With less sterically hindered primary amines a 1 1 ratio of amine to chloroform gives satisfactory results. Furthermore, by modifying the procedure, methyl and ethyl isocyanides may be prepared directly from the corresponding aqueous amine solutions and bromoform.7 These results are summarized in Table I. 

The ultrasonic preparation of thioamides from amides and phosphorus pentasulfide by Raucher(51) and of dichlorocarbene from chloroform and potassium hydroxide by Regen(52) are some of the more recent examples of nonmetallie applications. We were surprised to find that ultrasound greatly accelerates the reduction of haloaroma-tics by lithium aluminum hydride, permitting the reaction to be... 

Some a-eliminations have already been discussed, like the formation of dichlorocarbene from chloroform and base. Others will be presented in certain contexts later. 1,3-Eliminations are mentioned in the preparation of 1,3-dipoles such as diazoalkanes or a-diazoketones and nitrile oxides (Chapter 15). Chapter 4 is limited to a discussion of the most important eliminations, which are the alkene-forming, /3-eliminations. Note that /3-Eliminations in which at least one of the leaving groups is removed from a heteroatom are considered to he oxidations. Eliminations of this type are therefore not treated here hut in the redox chapter (mainly in Section 17.3.1). 

German chemists have used the method successfully for preparation of dichloro-cyclopropanes from olefins which yield little or no products when the dichlorocarbene is generaied from chloroform and potassium /-bntoxide. TTiey also generated dibromo-carbene in the same way. Cyclopropcnes are obtained in only low yields from acetylenes owing to side reactions. 

Of the many methods used for dichlorocyclopropanation of alkenes, the formation of dichlorocarbene from chloroform and base/phase-transfer catalyst and its subsequent reaction with an alkene is strongly recommended. In fact, since inception this method has been the most frequently used for the preparation of 1,1-dichlorocyclopropanes. ... 

A variety of methods have been tried for the preparation of hexachlorocyclopropane from tetrachloroethene and dichlorocarbene the chloroform/base/phase-transfer catalyst method fails, the chloroform/potassium fert-butoxide and sodium trichloroacetate/heat methods give 0.2 to 1.0% yield, using chloroform/85% solid potassium hydroxide at 100 to 110 °C for ca. 45 minutes the yield is 4.5% and finally the bromodichloromethyl(phenyl)mer-cury/heat method afforded the product in 83% yield. 

In the case of unsaturated alcohols, the double bond may effectively compete with the hydroxy group for the dichlorocarbene, yet the nature of the final product depends on the structure of the unsaturated alcohol and on the reaction conditions. From the preparative point of view, the chloroform/base/phase-transfer catalyst method gives the best results for the cyclopropanation of unsaturated alcohols (Houben-Weyl, Vol. E19b, p 1542). 

Alkynes react with various dichlorocarbene reagents to give 3,3-dichlorocyclopropenes 1, which can be hydrolyzed to cyclopropenones 2 in situ. The carbene reagents used are (A) chloroform, 50% sodium hydroxide, and triethylbenzylammonium chloride (TEBAC) (B) (bromo-dichloromethyl)phenylmercury (C) chloroform and potassium tert-butoxide and (D) chloroform and butyllithium. Although the yields of these reaction generally do not exceed 20%, a variety of cyclopropenones have been prepared by this method. The yields of biscyclo-propenones from diynes are very low. 

Dichlorocarbene. This base is useful for preparation of dichlorocarbene from chloroform. One advantage is that the reaction can be carried out in a homogeneous system (pentane, hexane, THF). Higher temperatures (65°) are necessary than when potassium f-butoxide is used, and the reaction is some-... 

Dichlorocarbene Dichloronorcarane can be prepared in about 75% yield from cyclohexene, chloroform, and an aqueous solution of sodium hydroxide in the presence of tri-n-butylamine or the hydrochloride as catalyst. Some other tertiary amines or quaternary ammonium salts are equally effective tetra- -butylammonium bromide, N-n-butylpiperidine, N,N-di-n-butylpiperidinium iodide. No primary or secondary amines were found to have this catalytic activity. 

Dichlorocarbene (generated in situ from chloroform) reacted with l,2 5,6-di-0-isopropylidene-a-D-glucofuranose in a phase-transfer system to give the rearranged product 6-chloro-6-deoxy-l,2 3,5-di-0-isopropylidene-a-D-glucofuranose, whereas 2,3 5,6-di-O-isopropylidene-a-D-mannofuranosyl chloride was obtained from the reaction of dichlorocarbene with 2,3 5,6-di-0-isopropylidene-a-D-manno-furanose. The a-D-mannofuranosyl chloride derivative was used to prepare the corresponding methyl and benzyl a-glycofuranosides and in the synthesis of a-linked disaccharide derivatives. 

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