Amines dihalocarbene reactions

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

REACTIONS OF DIHALOCARBENES WITH AMINES, IMINES, AMIDES AND RELATED COMPOUNDS... 

Predictably, the reaction of A V-disubstituted enamines [26-29] and non-conju-gated unsaturated amines with dihalocarbenes results in the exclusive formation of the dihalocyclopropane derivatives (see Section 7.3). Dichlorocarbene inserts into the a-CH bond of Af-alkyldibenzo[6,/]azepines [16], in addition to the expected electrophilic addition to the C=C bond (see Sections 7.2 and 7.3). 

The catalysts must supply the system with lipophilic cations in order to form, with required anions, ion pairs able to enter nonpolar media. The most typical catalysts are tetraalkyl ammonium (TAA) salts R4N+X, particularly those having at least 16 carbon atoms in the four R groups. Similar lipophilic catalysts are tetraalkylphosphonium and -arsonium or trialkylsulfonium salts, which are less available and usually less stable. They are therefore of negligible practical use. There are a few reports on the use of trialkylamines as catalysts in some two-phase reactions. Usually these amines are qua-ternized by a reactant actually these reactions are catalyzed by TAA salts. More complicated is the generation of dihalocarbenes with trialkylamines. The amines form, with the carbene, an ammonium ylide, which acts as a base in the organic phase. 

The catalytic action of tertiary amines, in particular tributylamine, used in place of a quaternary ammonium salt, is worthy of mention (for the mechanism of the action of tertiary amines in phase-transfcr-catalyzed reactions of dihalocarbenes, see ref 12). These catalysts... 

Besides addition to double bonds to give dihalocyclopropane derivatives—the most important reaction of dihalocarbenes—many other reactions of these active electrophilic species can be performed using PTC methodology, such as insertion into C-H bond, reactions with primary and secondary amines and with many other nucleophiles ... 

Crown ethers, cryptands, quaternary salts bonded to a polymer (Sects. 5.1, 5.2, 6) and finally free amines have been successfully used in carbene generation in two-phase systems. In the latter case, the mechanism is rather complex, and different interpretations have been advanced. However, the last step of the generation of the dihalocarbene probably does not differ substantially from the reaction of CHCI3, NaOH and quaternary salt In Table 16 are compiled some examples of addition and insertion of carbenes. 

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