Dichlorocarbene imine reactions

Chloropyrroline 86, arising from the reaction of imine 85 (R = Me) with dichlorocarbene and dimethyl maleate, with an excess of dichlorocarbene, gives pyridine 186 (40% per imine) [91MI1, 95ZOR(ip)]. Pyridine derivatives are also formed in the reaction of ketene imines with dichlorocarbene and activated ethylenes (see Scheme 19) (87KGS1336 88ZOR-1917). 

An interesting reaction was observed on phase-transfer generation of dichlorocarbene in the presence of mono- and 1,2-disubstituted hydrazines and dimethyl maleate. In this case the initially formed ammonium ylide 511 transforms to azomethine imine 512 followed by 1,3-dipolar cycloaddition to an olefin providing pyrazolines 513 96ISV(ip). 

The addition of carbenes and carbenoids to imines and nitriles continues to be a popular approach to aziridines and 2//-azirines. These processes have been well reviewed by Deyrup (B-83MI101-01). Dichlorocarbene and other dihalocarbenes have been added to a wide variety of imines to provide dihaloaziridines. A recent example is shown in Equation (64), illustrating the use of phase-transfer conditions <93H(36)69i). The treatment of azides with excess dichlorocarbene results in the formation of the 2,2,3,3-tetrachloroaziridines (92TL2339). Presumably, the azide is converted by dichlorocarbene to the imidoyl dihalide RN=CC12 which reacts further with dichlorocarbene. Transition metal-promoted reaction of a-diazoesters with imines provides 2-(alkoxycarbonyl)aziridines [Pg.46]

The reaction of imines with chloroform in the presence of KF or A1203 did not proceed at all, whereas the use of commercially available KF/A1203 led to the gem-dichloroaziridines. Although conventional methods for generation of dichlorocarbene require a large excess of chloroform, the present method is able to reduce the amount of chloroform considerably [4] (Scheme 5.2). 

The dichlorocyclopropanation of simple olefins is characterized by good yields, convenient reaction conditions and inexpensive reagents. When there is more than one isolated double bond in a substrate, products of both mono and multiple cyclopropanation are isolated unless a selective catalyst is used (see above). Examples of the simple dichlorocyclopropanation reaction are presented in Table 2.1. Examples of multiple dichlorocyclopropanation are recorded in Table 2.2. Imines also add dichlorocarbene and are discussed in Sect. 3.4. 

The reactions of dichlorocarbene with a variety of olefinic and acetylenic substrates have been discussed in Chap. 2. We wish now to turn our attention to the reactions of this species with a number of other substrates which either are non-olefmic or contain double bonds which do not constitute the major reactive function. The substrates considered here are alcohols, imines, amines, amides, thioethers, and hydrocarbons. With the exception of the latter, all of these species appear to react by initial coordination of the electrophilic carbene with a Lewis basic site. Subsequent reactions attributable to differences in the basic function or involvement with other reactive sites lead to differences in the chemistry of each substrate, and each is therefore considered separately. 

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