Salts vinamidinium

Vinamidinium salts have been used for the preparation of 2,3- or 2,5-disubstituted pyrroles. Thus, reaction of sarcosine ethyl ester with 18 results in an amine-exchange reaction at the least hindered position. Anion mediated cyclization and elimination of dimethylamine leads to 19 <96T6879>. 

Syntheses of fluoro-substituted pyrazoles continue to be of interest. Both 3- and 5-fluoropyrazoles (44 and 45, respectively) can be prepared from 43 <96JOC2763>. Treatment of 43 with hydrazine followed by N-alkylation provides 44, whereas reactions with monosubstituted hydrazines afford 45. The 4-(trifluoromcthyl)pyrazoles 47 are obtained from J-trifluoromethyl vinamidinium salt 46 <96TL1829>. The 5-trifluoromethyl-3-carboethoxypyrazoles 49 are obtained from the 1,3-dipolar cycloadditions of trifluoromethyl alkenes 48 with ethyl diazoacetate <96T4383>. 

Cycl[3.2.2]azines may also be obtained by the cycloaddition of a bifunctional three-carbon unit to a 3//-pyrrolizine. Vinamidinium salts have been used for this purpose <1984CB1649>, although the reactions require the use of a strong base (sodium hydride) and extended reaction times. They appear to proceed via a stepwise mechanism, since intermediates (the conjugated enamines 354 and 355) have been isolated in certain cases (Scheme 94). 

Regiospecific reactions occur between unsymmetric diamines and un-symmetric vinamidinium salts [81JCR(S)356 81JCS(P1)726]. 

In addition to vinamidinium salts, 5-aza-l-oxapentadienium salts, themselves obtained by alkylation of oxoenamines, also react rapidly with 1,2-diamines under mild neutral conditions to give good yields of dihydrodia-zepinium salts [78JCS(P1)1453]. 

The use of derivatives of dicarbonyl compounds such as diazapentadienium or vinamidinium salts, e.g. (167) and (168), is a recent development which offers advantages in providing access to dihydrodiazepines (164) not easily prepared in other ways (78H(11)550, 78JCS(P1)1453>. 

The Kyoto group has developed some interesting chemistry based upon this readily available alcohol. / -Fluoro vinamidinium salts with potential for the synthesis of fluorinated heterocycles were prepared according to Eq. (89) [265]. Treatment of the tosylate of tetrafluoropropanol with n-butyllithium achieves regioselective dehydrofluorination a short reaction time appears to be critical [266]. 

Vinamidines and Vinamidinium Salts — Examples of Stabilized Push-Pull Alkenes D. 

Unsymmetrical vinamidinium salt 137 can be cyclized with 51 at low temperature to give the 7-substituted isomer 138, but at higher temperature isomers 138 and 139 were both obtained. When the chloropropeniminium salt 136 was used under similar conditions, compound 138 was formed. The... 

Reactions with iminium salts are also reported. The triflate 47 reacts with anilines to yield 2-trifluoroquinolines (Equation 164) <1999EJ0937>, whereas condensation of the vinamidinium salt 48 with anilines leads to 3-for-mylquinoline derivatives (Equation 165) <2001S1351 >. 

Vinamidinium salts are important intermediates in the synthesis of heterocycles. The 2-chloro-l,3-bis(dimethylamino)trimethinium hexafluorophosphate salt has been used in the preparation of the highly selective Cox-2 inhibitor etoricoxib (Scheme 1). This method describes a straight-forward preparation of the hexafluorophosphate salt which is a crystalline, thermally and shock-stable, non-hygroscopic solid. The submitters have extensively studied the preparation of vinamidinium salts and demonstrated that the method is applicable to substituted acetic acids that contain an electron-withdrawing group (Table 1)." The annulation reaction is also general and useful for the preparation of pyridines, pyridones and pyridine N-oxides. ... 

SeIvi, S., Perumal, P. T. Synthetic utility of the Vilsmeier reaction more vinamidinium salts. Synth. Commun. 1999, 29, 73-77. 

It is very important for preparative performances that such real and formal cyclizable 1-aminohexatrienes are easy to obtain by aldol- or Knoevenagel-like condensations of various vinamidinium salts (7) with a broad spectrum of C—H acid methyl and methylene compounds, as we will see in a following section. 

If we construct a hexatriene we can perform this in a fictitious manner by means of a substitution reaction in two ways methyl anion by pentadienyl cation (Ci + C5 combination) or allyl anion by allyl cation (C3 + C3 combination). In each case the one partner provides two rr-electrons, the other partner four 7r-electrons to the six-7r-electron system hexatriene. Such an imaginary reaction can indeed be realized simply by an aldol- or Knoevenagel-Iike condensation of a vinamidinium salt 10 ... 

Table 2, Vinylogues of vinamidinium salts ( pentamethinium salts )...

The catalogue of vinamidinium salts (7) used also can be extended to mono-and bicyclic derivatives (7 o-s), which we prepare in the manner mentioned (Section III.A.) from corresponding ketones as outlined here for the acenaphthylene compound (7 s)16). 

But this has an essential restriction some of the used vinamidinium salts (7) are sensitive and may be decomposed by treatment with strong base, e.g., sodium me-thoxide. Especially such salts possessing methyl or methylene groups at odd-numbered, electron-dificient positions of the vinamidinium system tend toward complex self-condensations a proton abstraction to a diene amine may occur, followed by attack of the unaltered ion ... 

On the other hand, the vinamidinium salts (7) always react with their least-substituted iminium carbon position. 

Although Table 7 is by no means exhaustive, it gives a good impression of the versatility of the method. 9,10-Dihydrophenanthrenes, for instance, may be formed using the bicyclic allylcyanides, (24g) or (24 h) and open-chain vinamidinium salts (7a-n) or open-chain allyl derivatives, e.g., (23 a) or (23 b), and the bicyclic vinamidinium salts (7q) or (7r). Thus, 9,10-dihydrophenanthrene- 1,3-dicarbonitrile (Table 7, No. 19) could be synthesized in two ways ... 

Appropriate nitro-allyl derivatives for condensation to hexatrienes are usually not easily available, with the exception of nitromethyl-l-cyclohexene and nitro-methyl-l-cycloheptene (34)43. Like nitromethane, 34) does not condense with vinamidinium salts (7) and sodium methoxide, but yields insoluble sodium salts. 

Likewise the reactive methyl groups in 2-methylchromone (19) and 2,6-dimethyl-4-pyrone are also susceptible to condensation with vinamidinium salts (7), as are their vinylogues (compare Section B. 1.). The colored condensation products (42) smoothly cyclize to xanthones (43) ... 

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