General reactions 2-imidazolines

Imidazolines are also formed in silver cyanide-catalyzed cyclization of alkyl isocyanides with aliphatic diamines (Scheme 103).169 This simple synthesis can be applied in a general way with difunctional nucleophiles and has been used to prepare benzimidazoles, oxazoles, thiazoles, and oxazines.169 It is suggested that transient carbene complexes are formed in these reactions (cf. 87 in Scheme 103) but further work is required to ascertain the mechanism and scope of these processes. 

The TBP structures of 9 I2 and 11 2I2 are noteworthy, since iodine adducts of selenides are predicted to be MC based on the general rule (x(Se) (=2.48) > xCO (=2.21)). This must be the reflection of the high ability of the imidazoline ring to donate electrons to Se by the formation of the stable cyclic 6ji system. It will decrease xeff of Se in 9 and 11 to give TBP with iodine. Since the electronic conditions in 10 must not be so different from those in 9 and 11, they should not be responsible for the different structures of the adducts. This working hypothesis is supported by DFT calculations.38 Therefore, the crystal packing effect must play a crucial role in determining the structures of the iodine adducts of 9-11. The reactions are followed by spectroscopic and conductometric methods.37... 

In many cases the synthesis of NHC complexes starts from iV,A/ -disubstituted azolium salts. Imidazolium salts as precursors for imidazolin-2-ylidenes are generally accessible by two ways complementing each other (i) nucleophilic substitution at the imidazole heterocycle or (ii) a multicomponent reaction building up the heterocycle with the appropriate substituents in a one-pot reaction. 

Synthesis of l-hydroxy-3-oxyimidazolines from a-hydroxylaminooximes has been reviewed " . Therefore, in the present work it will be described very briefly. In general, the reaction of oximes 136 with aldehydes, ketone or triethyl orthoformate leads to imidazolines 137 or 138, respectively (equation 60). 

Substituted 2-amino-2-imidazolines (13, R = H) may be prepared by a useful general method developed by Bloom21 by the reaction of thiopseudourea hydriodides (12) with ethylenediamine. Another... 

Most of the amphopropionate surfactants produced are of the amphodipropionate type, 2 mol of methyl acrylate or sodium acrylate added per mole of imidazoline. Depending on the reaction conditions, 1 mol of acrylate can add to the fatty R group at the alpha carbon. Upon hydrolysis of the imidazoline, the second reacts with the liberated secondary amine to produce the beta alanine derivative. If methyl acrylate is used, the methyl ester of the amphoteric surfactant is formed. An equimolar amount of sodium hydroxide is added to effect saponification to the sodium salt of the surfactant. Methanol is formed as a by-product and it is generally left in the final product as part of the solvent system. 

It is a general rule that imidazoles and benzimidazoles are resistant to Friedel-Crafts reactions. This is not surprising since such basic compounds must be markedly deactivated in the presence of Lewis acids. Imidazolin-2-ones appear to be an exception and apparently possess sufficient activation to react. Reactions between imidazoles and Af-methylfor-manilide and phosphoryl chloride are also unproductive. With 4,5-diphenylimidazole, phenyl isocyanate at 80 °C gives products of both N- and C-substitution, but in boiling nitrobenzene only the latter (86) is formed. 2-Methyl-4-phenylimidazole gives (87) under the same conditions, and 1,3-diphenylimidazolium perchlorate is transformed by potassium t-butoxide into a ylide which reacts at C-2 with phenyl isothiocyanate. Sufficient activation is present in l-methyl-2-phenyl-4-phenylaminoimidazole for it to react by substitution at C-5 with acetic anhydride (71JOC3368). 

The two general methods for preparation of 4-imidazoline-2-thiones are the reaction of acyloins with thioureas and the acid hydrolysis of alkyl- or arylthiureidoacetals. The above reactions have been summarized in a review by Hofmann. Aren and Bite recently reported that the 2-phenyl-2-thiureido-l,3-indanediones (17) undergo rearrangement in strong acid to produce in high yield a series of 4-imidazoline-2-thiones (18). 

These studies have shown that the palladium catalyzed coupling imines, CO and acid chlorides is a viable and general route for the synthesis of a new class of peptide-based imidazolines. Mechanistic studies suggest this four-component coupling reaction proceeds via the in situ formation of Miinchnone intermediates, which undergo cyclization with imines in the presence of acid to yield the ob-... 

In another example, the hydrogenation of the azapenam (55,6/ )-6-methoxy-2,2,6-trimethyl-l,4-diazabicyclo[3.2.0]heptan-7-one (154), prepared by reaction of a pentacarbonyl chromium carbene complex with liV-Boc-4,4-dimethylimidazoline, in the presence of 1.1 equiv. of racemic camphor sulfonic acid resulted in the cleavage of the Boc group and ring expansion of the azapenam to hexahydro-3,3,6-trimethyl-6-methoxy-5//-l,4-diazepin-5-one (155) in 71% yield <92JA5010>. It was pointed out that the ready availability of a variety of substituted chromium carbene complexes and imidazolines would make this a general route to this class of diazepine. 

Mohammadpoor-Baltork and colleagues also investigated the scope and generality of this catalytic system by the synthesis of 2-imidazolines (20) (Table 1.9, entries 1-6) and 2-thiazolines (21) (Table 1.9, entries 7-12). The reactions were carried out starting from different types of arylnitriles and ethylenediamine or 2-aminoethanethiol, respectively, under the same reaction conditions used in the synthesis of 2-oxazolines, obtaining the corresponding derivatives in good to excellent yields. 

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