Substituents imino-carbon

The C=N bond of simple imines possesses modest reactivity toward intermolecular radical additions, so such acceptors have rarely been exploited. To enhance their reactivity toward nucleophilic radicals, electron-withdrawing groups at the imine carbon have been effective, as demonstrated by Bertrand in radical additions to a-iminoesters prepared from chiral amines [25]. Also, more reactive oxime ethers have been exploited extensively for radical addition, mainly through the longstanding efforts of Naito [26]. In most cases, stereocontrol has been imparted through the substituents on the imino carbon chiral O-substituents on oximes for stereocontrol were ineffective, presumably due to poor rotamer control [27, 28]. 

In N-aryl compounds YZC=NAr (for instance, types J, K, L, Table 6) bearing two substituents Y, Z on the imino carbon, the plane of the aryl group is probably rotated with respect to the C=N— C plane so as to relieve steric interactions. Such a conformation permits (p—p)n conjugation of the nitrogen lone pair with the aromatic n system. 

Alkoxy or dialkylamino substituents were introduced into the 2-position (Scheme 9). " These OZO derivatives are not one of the classes of cyclic imino ethers, but 2-alkoxy-2-oxazoline is classified into a cyclic imino carbonate and N,N-dialkylamino-2-oxazoline into a cyclic pseudo-urea. These monomers polymerized to yield pseudo-polyurethane and pseudo-polyurea, respectively. 

Changing the identity of the ortho substituent of aryl azides dramatically influences its reactivity toward transition metals. Shen and Driver discovered that substitution of a vinyl group with an iminyl moiety enables Fe(II)-catalyzed benzimidazole (65) formation (Scheme 16.29) [48]. It was proposed that coordination of iron(II) bromide to the imino nitrogen of 64 facilitates the C—N bond formation through nucleophilic attack of an azido nitrogen to the activated imino carbon, leading to B. Expulsion of N2 followed by tautomerization affords the benzimidazoles 65. 

There have been ab initio studies of the bonding for a series of imino and amino phosphorus molecules,15 and for the phosphonium ylides (8).14 The anion character of the ylidic carbon is intermediate between that of olefinic and substituted carbanions. Polarisation of the H3P group has a stabilising effect. The influence of the substituent X on the inversion of the carbanion and also the tendency of the molecule to dissociate to carbene and phosphine is also discussed.14 CNDO/S MO calculations on the... 

A new class of metaphosphinates, namely iminomethylenephosphoranes (1 with R = N(SiMe3)2, X = NSiMe3) is accessible by reaction of diazoalkanes with imino-phosphines (SiMe3)2N—P=N—SiMe3. Depending on the substituents on the methylene carbon atom, compounds of this class are either stable or dimerize across the P=C or P=N double bond 141). 

Oxidative Animation of Nitrones to a-Amino-Substituted Nitroxyl Radicals Similar to the oxidative methoxylation reaction, oxidative animation of 4H -imidazole TV-oxides, in amine saturated alcohol solutions, give stable nitroxyl (282), nitronyl nitroxyl (283), imino nitroxyl (284) and (285) radicals with the amino group at the a-carbon atom of the nitroxyl group (Scheme 2.107) (520, 521). The observed influence of substituents on the ratio of animation products at C2 and C5 atom is close to the ratio observed in the previously mentioned oxidative methoxylation reaction. It allows us to draw conclusions about the preference of the radical cation reaction route. 

A similar process involving an all-carbon cyclic system has also been investigated [59]. Other examples involving the prototropic rearrangement of enediynes having an imino or a keto substituent at the propargylic position to form the corresponding enyne-allenes have also been observed [60, 61]. 

The basicity of compounds containing the amidino group N=C—N depends on the substituents at the three sites (both nitrogens and the amidino carbon atom) and the protonation site is the imino nitrogen atom75. It has been shown76 that, at any of the three sites, in the series of monosubstituted amidines, their pKa values obey Hammett s equation. 

Several reports deal with studies of rearrangement rates related to various electron-donating and electron-withdrawing substituents on the ring carbons and/or ring nitrogen in l,2-dihydro-2-imino-l-methylpyrimidine. 

Cyclocarbonylation of o-iodophenols 503 with isocyanates or carbodiimides and carbon monoxide in the presence of a catalytic amount of a palladium catalyst (tris(dibenzylideneacetone)dipalladium(O) Pd2(DBA)3) and l,4-bis(di-phenylphosphino)butane (dppb) resulted in formation of l,3-benzoxazine-2,4-diones 504 or 2-imino-l,3-benzoxazin-4-ones 505 (Scheme 94). The product yields were dependent on the nature of the substrate, the catalyst, the solvent, the base, and the phosphine ligand. The reactions of o-iodophenols with unsymmetrical carbodiimides bearing an alkyl and an aryl substituent afforded 2-alkylimino-3-aryl-l,3-benzoxazin-4-ones 505 in a completely regioselective manner <1999JOC9194>. On the palladium-catalyzed cyclocarbonylation of o-iodoanilines with acyl chlorides and carbon monoxide, 2-substituted-4f/-3,l-benzoxazin-4-ones were obtained <19990L1619>. 

Method Cis based on intramolecular cyclization of 2-aminothiophenes containing a substituent with the electrophilic y-carbon atom at position 3. This class of compounds, for example, amines 50, can be prepared by multicomponent cascade heterocyclization of phenyl isothiocyanate, CH-acids, and alkylating agents (1991SL229, 1992G147, 1992M341, 2001PS215). Cyclization of compounds 50 affords 6-oxo(imino)-6,7-dihydrothieno[2,3-Z>]pyridines 51 as the final products. 

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