8- aziridinium salts

The conversion of 8 to 207 probably proceeds via the aziridinium salt 208, which can suffer opening 144) to 209. The latter is readily hydrolyzed to the amide (207). 

Another class of nucleophilic addition to iminium salts can be found in the addition of diazoalkanes. These are of great interest since they were known to add and then reaet further to form three-membered rings as in the case of C=S, C=0, and C=C functions 103). Leonard and Jann 104-106) found that treatment of iminium perchlorates with diazomethane and other diazoalkanes yielded aziridinium salts. Treatment of an iminium salt such as N-cyclohexylidinepyrrolidinium perchlorate (66) with diazomethane yielded a new product whose structure was established by spectral and chemical means to be 5-azoniadispiro[4.0.5.1]dodecane perchlorate (67). The UV spectrum was devoid of any absorption above... 

A representative list of aziridinium salts prepared by reaction of iminium salts with diazomethane is given in Table 9. The reactions of aziridinium salts are many and varied, but will not be given here since their synthetic utility has been explored and reported elsewhere 109,112-114). The products from the reaction of iminium chlorides and diazomethane are reported in Table 10. Many more examples are available in the literature 16). 

A more general aecess to the synthetie potential of aziridinium salts is found in the reactions of imonium salts with diazomethane 225,524,525, 536). 

The transformation proceeds with excellent stereoselectivity by kinetic formation of the 2,5-trans-disubstituted pyrrolidine 2-328 [182]. The tertiary amine can now initiate a nucleophilic backside displacement of the vicinal iodide in 2-328, leading to an aziridinium salt 2-329 [183]. This event ensures a net retention of the stereochemistry at C-13 in the following attack of the ester carbonyl in the butyrolactone ring closure to give 2-330. 

Azacyclonol, 47 Azaphenothiazine, 429 Azepinamide, 137 Azetidone, synthesis, 419 Aziridinium salt, 79 Azlactone, 96 Azomycin, 238... 

A. Compounds with One Nitrogen Atom 1. Aziridinium Salts... 

Arylaziridinium salts exhibit an unusual behavior in aqueous buffer solution in that the half-wave potentials become more negative on introduction of electron-attracting groups this is contrary to expectation. The abnormal substituent effect for aziridinium salts can be interpreted as involving development of a partial positive charge at the benzylic carbon before electron transfer.182... 

One of the few aziridinee which is readily alkylated te give s stable quaternary aziridinium salt is 1 -azaapiro[6.2Joctane1 . i (Eq. 46). Some unsuccessful attempts to obtain stable quaternary aziridinium salts by alkylation of an azirjdine with alkyl halides have been reported.18 ... 

A novel synthesis of relatively stable quaternary aziridinium salts has been introduced by Leonard854 Ternary iminlum perchlorates (obtained by treatment of the corresponding enamine with perohlorti acid) react with diazomethane to give the aziridinium perchlorate... 

Nucleophilic Ring opening. Opening of the ethyleneimine ring with acid catalysis can generally be accomplished by the formation of an intermediate aziridinium salt, with subsequent nucleophilic substitution on the carbon atom which loses the amino group. In the following, R represents a Lewis acid, usually H + A = the nucleophile. 

Because of the rapid ring opening by the nucleophile, a ziridinium salts cannot usually be isolated. However, in a few cases it is possible to isolate such compounds (54), eg, at low temperatures, when the aziridinium salts are sparingly soluble or where there is steric hindrance to substitution. Stable ethyleneiminiiim salts can be prepared by reaction of ethyleneimine with acids not containing nucleophilic anions, for example HBF4 (55). 

Arylpropanoic acids, 321 Arylsulfonyltetrazoles, 359 AT-125, 188 Aurentiacin, 72 Azasulfenylation, 204—205 Aza-Wittig reaction, 588 Azetidinones, 39-40, 125 AzidotrimethyIsilane, 32 Aziridines, 453 Aziridinium salts, 215 Aziridinones, 562... 

Several studies on the reactions and preparation of aziridines have been published. The ring opening of 2-substituted aziridines, accomplished by first converting them into aziridinium salts by reaction with a benzyl bromide and then attack of the bromide counter ion, gave only one bromide in a regio- and stereo-specific reaction.43 Since attack by the bromide ion of the aziridinium salt only occurred at the most substituted carbon with an inversion of stereochemistry, it was concluded the reaction occurred by an SN2 mechanism. This was supported by calculations at the MPWBlK/6-31+G(d) level of theory for reactions featuring two solvating acetonitrile molecules embedded in an acetonitrile matrix. 

Diazomethane reacts with the salts of enamines to yield aziridinium salts.327 327a ThusiV-cyclohexylidenepyrrolidinium perchlorate yields 2,2 -pentamethylene-1,1 -tetramet hyleneaziridinium perchlorate (101). Hydrogenation over Adams catalyst cleaves the bond between the quaternary nitrogen atom and the methylene group to form A-(l-methylcyclohexyl)pyrrolidinium perchlorate (102). 

Alkylation of aziridine in base gives the N-substituted aziridine as you might expect, but a second alkylation leads to a positively charged aziridinium salt that opens immediately to the useful bro-moamine. In this case, the product is an intermediate in the synthesis of two natural products, san-daverine and corgoine. 

Despite this tendency, examples of alkylation, acylation, sulfonylation, halogenation, silylation, and phosphorylation of aziridines at nitrogen abound. Aziridinium salts can be prepared by further alkylation of the aziridine nitrogen. Aziridines can also be alkylated on nitrogen with epoxides producing -hydroxyamines. 

Nitrogen heterocycles, preparation from aziridinium salts ... 

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