Iminium salts cyclic

Nuclear magnetic resonance has revolutionized structure determination of iminium salts. A compilation of various resonances for acyclic and cyclic iminium salts are given in Tables 3 and 4 for comparison purposes and for determination of trends. It should be noted that the simplest symmetrically... 

A wide variety of organoalkynyl derivatives of cotarnine hydrochloride, a cyclic iminium salt with rich biological activity, were prepared from the direct alkynylation of cotarnine hydrochloride using silver(l) alkynyls.180 Substituted enynes were prepared from the coupling reactions of silver alkynyls with the palladium allyl intermediates, which was... 

It has been shown that phenylselenyl halides easily reacted with 0-allyl oximes 221 to give cyclic iminium salts 222, which by reaction with water afforded isoxazolidines 223 in moderate to good yields (equation 96) . Compounds 222 can be reduced in situ by sodium borohydride to produce Ai-alkyl-substituted isoxazolidines 224 in 50-95% yields . ... 

The formation of NNN, NNK, and NNA from nicotine probably involved the intermediacy of cyclic iminium salts, as shown in Figure 5 (28). These salts can undergo hydrolysis to the free amines which are nitrosated, or at near neutral pH, can be directly nitrosated to give nitrosamines. The formation of nitrosamines from iminium salts under neutral conditions has been demonstrated in at least two studies and is of interest because iminium salts are known to be intermediates in the mammalian metabolism of nicotine (26,29,30,31). The possibility that tobacco bacteria could nitrosate nicotine via this pathway is currently under investigation. 

A cyclic iminium salt was hydrogenated using an Ir catalyst with (S)-(3,5-fBu)-tLANOP, an amidophosphinephosphinite ligand, in the presence of (n-C4H9)4NI under 100 atm of H2 to give the S ammonium salt in 86% ee and in 46% yield, accompanied by 54% of the decahydroisoquinoline derivative (Scheme 10) [23]. 

The cyclization of O-allyl oximes 1, performed with diphenyl diselenide/ammonium thiosulfate/ trifluorosulfonic acid or phenylselenenyl bromide, gave cyclic iminium salts 2 via an intramolecular antt -addition mechanism. By addition of water to the reaction mixture, 3-substi-tuted isoxazolidines 3 are formed in good yield. When the salts 2 were prepared by using phenylselenenyl bromide, A-alkyl 3-substituted isoxazolidines 4 were afforded in good yield by reduction of 2 with sodium borohydride in methanol247-249. 

A completely new cyclization reaction is the PhSeBr promoted conversion of alkenyl nitrones into 1,2-oxazines, which was recently reported by Tiecco [79]. This are the first examples to use alkenyl nitrones to effect ring closure reactions induced by electrophilic reagents. As indicated in Scheme 20, the nitrones 130 and 134 react with PhSeBr to give the cyclic iminium salts 131 and 135, respectively. These intermediates suffer attack by nucleophilic reagents at the partially positive carbon atom. The nature of the final products depends on the structure of the starting nitrone and of the nucleophile employed. Thus, the intermediate... 

The piperidine alkaloids were mentioned in the chapter (p. 1418) where the pathway was described as similar to that of the pyrrolidine alkaloids . We can follow the same reactions starting from lysine instead of ornithine. The first stage produces the cyclic iminium salt fi om lysine by decarboxylation with pyridoxal. 

The most obvious derivative of nicotinic acid that is nucleophilic in the 3-position would be an enamine, easily made by reduction. Let us try that first with the cyclic iminium salt to see if we can... 

While the addition of organometallic reagents to acyclic or cyclic imines (43) is often compromised by poor imine reactivity, these reagents readily condense with structurally diverse, more electrophilic imini-um salts (44), bearing a positive charge on the nitrogen atom, to provide substituted tertiary amines (45 Scheme 6). A review of the literature describing additions to cyclic iminium salts prior to 1966 is avail-... 

Addition to cyclic iminium salts has been utilized in alkaloid synthesis. A zinc-promoted reductive coupling reaction of iminium salts and alkyl halides has been reported by Shono et al. (Scheme 8). Evidence delineating the mechanistic course (organozinc addition or electron transfer reaction) of the addition has not been established. In contrast to organolithium or Grignard additions, aromatic halogen and alkoxycarbonyl substituents are compatible with this methodology. The intramolecular version of this reaction has been employed for the synthesis of tricyclic amines (53 equation 9). 

In the alkylation of lactams the equilibrium position also lies at the side of the iminium compounds (80 equation SO), so it is not surprising that 4- to 12-membered ring lactams have been methylated by dimethyl sulfate to produce the corresponding cyclic iminium salts. "... 

Benzo[c]cinnoline is a weak base with a of 2.2 in water and 1.6 in 50% aqueous ethanol.Cryoscopic measurements show that it is dipro-tonated to some extent in 100% sulfuric acid. Well-defined quaternary salts result from heating benzo[c]cinnoline with alkyl halides and sul-fates. These are reported to decompose on treatment with ammonia, regenerating benzo[c]cinnoline, but apparently nucleophilic displacements of halogen by amines have been carried out on certain highly substituted examples in the synthesis of cationic dyestuffs. Quaternizations of benzo[c]cinnoline with a,a)-dibromo-propane and -butane are accompanied by hydrogen bromide elimination to give the cyclic iminium salts 40 and 41. When 40 is dehydrogenated, or merely refluxed in ethanol. 

Preformed cyclic /V,A-dialkyliminium salts i.e. where a ring Joins the a-caibon and positively charged nitrogen) have been used in enolate condensation reactions. The number of examples, however, is rather limited, probably because of complications arising through abstraction of enolizable protons. A -Dehy-droindolizidinium salt (69) represents one of the few examples of an enolizable, cyclic A, -dialkylimi-nium salt known to react with an enolate (equation 8). The use of a soft zinc enolate in this reaction may be crucial. The relative stereochemistry of the resulting 3-amino ester (70) is undefined. /V-Alkyl-3,4-dihydroisoquinolinium salts e.g. 71), a class of nonenolizable, cyclic iminium salts, have had extensive applications in the total synthesis of protoberberine and phthalide isoquinoline alkaloids. A review by Pai and coworkers has covered much of this work. In a more recent application by Yamazaki and co-... 

SCHEME 237 Transformation of pseudoephedrine carboxamides into cyclic iminium salt. 

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