Amidines alkylation

Amidines and related systems such as guanidines react with a-halogenoketones to form imidazoles. a-Hydroxyketones also take part in this reaction to form imidazoles, and a variety of substituents can be introduced into the imidazole nucleus by these procedures. Reaction of the a-halogenoketone (73) with an alkyl- or aryl-substituted carboxamidine (76) readily gave the imidazole (77) (01CB637, 48JCS1960). Variation of the reaction components that successfully take part in this reaction process is described in Chapter 4.08. 

One of the best methods of synthesis of isothiazoles is by direct oxidation of y- iminothiols (169) or their tautomers. The reaction is capable of many ramifications and is represented by the general equation shown in Scheme 27. The substituents represent a wide range of groups. Thus, iminothioamides (169 R = NH2) are oxidized to give 3-alkyl-5-aminoisothiazoles (170 = NH2), amidines (169 R = NH2) produce 3-amino compounds,... 

Reaction of pyridinium-A -(2-pyridyl)amidine (402) and alkyl haloace-tates in the presence of K2CO3 afforded a mixture of 4-oxo-4/f-pyrido[l, 2-u]pyrimidine-2-carboxylates 407 and 2-aminopyridine derivatives 406 through intermediers 403- 05, as depicted in Scheme 15 (00TL5837). Compound 406 could be cyclized on the action of heat or silica gel into 407. The best yield was achieved in the case of ethyl bromoacetate. 

The chelated lithium anions 1 and 2, derived from enantiomerically pure tetrahydroisoquino-line-amidines or -oxazolines, exhibit high induced stereoselectivity in alkylation reactions (Section D.l.1.1.1.3.1.). 

Gallium compounds that incorporate amidinate ligands have been studied because of their potential use as volatile precursors to nitride materials.The two most common classes of Ga amidinate compounds, however, are [RC(NR )2]GaX2 species, X = Cl, alkyl I in Scheme 32), in which one amidinate... 

Interesting new sulfido complexes of tin have been prepared by the reaction of styrene sulfide with the N-alkylated tin(II) amidinate complexes Sn[RC(NCy)2]2 (Cy = cyclohexyl R = Me, Bu ). The products exhibit two very different bonding modes for the sulfido ligands in one case, S = Sn[RC(NCy)2]2/ a terminal Sn = S moiety was found while in the other case the bridging... 

Homoleptic lanthanide(III) tris(amidinates) and guanidinates are among the longest known lanthanide complexes containing these chelating ligands. In this area the carbodiimide insertion route is usually not applicable, as simple, well-defined lanthanide tris(alkyls) and tris(dialkylamides) are not readily available. A notable exception is the formation of homoleptic lanthanide guanidinates from... 

As shown in Scheme 94, the fj -styrene zirconium complex Cp Zr (f/ -PhCHCH2)[MeC(NPr )2] also served as starting material in the synthesis of alkyl-substituted 1,3-diene complexes of (pentamethylcyclopentadienyl)zirco-nium amidinates. NMR spectroscopy as well as single-crystal X-ray analyses of these complexes revealed that they are best described by the Zr(lV) a, n-metallacyclopent-3-ene limiting resonance form rather than as Zr(ll) f/ -diene complexes. ... 

The polymerization of methyl methacrylate (MMA) by Cu(ll) amidinate complexes (Scheme 222) in combination with alkyl aluminum complexes has been reported. The preferred alkylating agent is methylalumoxane (MAO) in... 

Thus unsubstituted (R=H) and substituted (R = alkyl) non-stabilized diyiides 1 react with phenylisocyanate and dicyclohexylcarbodiimide (R NCX), leading to the formation of new monoylide type intermediates. These last ones react in situ with carbonyl compounds through a Wittig type reaction leading respectively to a,)8-unsaturated amides 2 and amidines 3, with a high E stereoselectivity, the double bond being di- or tri-substituted [48,49]. By a similar reactional pathway, diyiides also react with carbonic acid derivatives, with the synthesis as final products of -a,/l-unsaturated esters 4 and acids 5 [50]. 

Reactions of Alkyl 4-Chloro-3-trimethylsilyloxycrotonates with Amidines to Give Alkyl lmldazole(4,5]-acetates... 

Because esters 745 a, b of imidazole-acetic acid are unstable when stored for long periods, owing to intramolecular catalysis by the imidazole moiety, the esters should be converted into their salts or free acids and stored as such. Only tert-butyl imidazole-(4,5)acetates derived from tert-butyl 4-chloroacetoacetate seem to be stable [232, 233]. N-alkyl-substituted amidines give rise to a mixture of alkyl N-alkylimidazole-4- and 5-acetates [232, 233]. 

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