Synthesis of N-(tosylmethyl)carbodiimides and their application in the synthesis of 2-amino-1,3-oxazoles from aldehydes

Jeuing, H.J.; Wildeman, Jurjen; NISPEN, S. P. J. M. VAN; Leusen, A. M. Van

doi:10.1021/jo00323a018

Cited by 29 publications

(7 citation statements)

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“…Melting points and 1 H NMR spectral data of the aminooxazoles 4a,b,d,f,g correspond to literature data, and for previously unknown compound 4c,e we obtained satisfactory data of elementary analysis. Structure of most oxazoles 4 was confirmed by 13 C NMR spectra and mass spectra (which are absent in the literature), and the structure 4b was proved by X-ray analysis ( The are only few alternative methodologies to prepare 2amino-5-aryloxazoles: Curtius rearrangement of oxazolyl-2-carboxylic acids hydrazides, 17 multistep synthesis starting from N-(tosylmethyl)-N¢-tritylcarbodiimide, 18 and condensation of a-bromoketones with N-cyanourea. 19 Hence the strategy proposed in this communication, involving simple sequence with high yields and requiring cheap materials, may serve as a competitive complementary route to the class of compounds 4.…”

Section: Conversion Of Oxazolo[32-a]pyrimidinium Salts 3 To 2-amino-mentioning

confidence: 95%

Novel and Efficient Synthesis of 2-Aminooxazoles from Pyrimidin-2(1H)-one

Alifanov¹,

Бабаев²

2007

Synthesis

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Stepwise conversion of pyrimidin-2(1H)-one to 2-amino-5-aryloxazoles via oxazolo[3,2-a]pyrimidinium salts is reported. The sequence involves, (i) regioselective N-alkylation of pyrimidone by phenacyl bromides, (ii) cyclization of obtained 1-(2-aryl-2-oxoethyl)pyrimidin-2(1H)-ones into oxazolo[3,2-a]pyrimidinium salts under the action of fuming sulfuric (or triflic) acid, and (iii) reaction of the obtained salts with hydrazine leading to 2-amino-5-aryloxazoles.In our previous investigation 1 we described a simple route to 5-aryloxazoles IVa bearing a w-aminodienyl residue by ring opening of bicyclic oxazolo[3,2-a]pyridinium salts IIIa (Scheme 1), which in turn can easily be obtained from 2-pyridone Ia via N-phenacyl-2-pyridones IIa. The overall simplicity of this methodology to obtain a substituted five-membered azole (like IVa) from a six-membered azine Ia via bridgehead azolo-azine IIIa (rarely used in heterocyclic synthesis) stimulated our interest to expand this strategy to the related family of pyrimidine derivatives. The retrosynthetic sequence of the suggested conversions is shown on Scheme 2.One would expect that similar transformations starting from pyrimidin-2(1H)-one (1, 2-pyrimidone) and involving N-phenacyl derivatives IIb and oxazolo[3,2-a]pyrimidinium salts IIIb may lead to unstable oxazolylsubstituted aza-dienes IVb, which, therefore, could be precursors of 2-aminooxazoles V. In this communication we confirm this idea and report our first successful preparation of 5-aryl-2-aminoxazoles V starting from pyrimidone 1. The overall sequence shown in Scheme 2 has never been realized, although some related reactions have been briefly discussed in the literature. N-Phenacylation of Pyrimidin-2(1H)-one (1)The reaction of 2-pyrimidone 1 and its derivatives with ahalogenocarbonyl compounds is poorly investigated in the literature. There are only two examples of phenacylation in the 2-pyrimidone series, namely for 5-chloro-4-phenyl-2-pyrimidone 2 and the sterically hindered 4,6-dimethyl-2-pyrimidone. 3 Regarding the parent pyrimidone 1 only reactions with diethylacetal of bromoacetaldehyde 4 and chloroacetic acid derivatives 5 have been studied. In all these cases exclusive formation of the N-alkyl isomer was observed. Several 4-aryl-N-phenacyl-2-pyrimidones were prepared from a-aminoketones by an alternative strategy, not involving the alkylation step. 6

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Section: Conversion Of Oxazolo[32-a]pyrimidinium Salts 3 To 2-amino-mentioning

confidence: 95%

Novel and Efficient Synthesis of 2-Aminooxazoles from Pyrimidin-2(1H)-one

Alifanov¹,

Бабаев²

2007

Synthesis

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“…The result is in striking contrast with our previous convergent reaction giving 5-acyl-2-iminothiazolines from lithium alkynethiolates, carbodiimides (R 1 , R 2 = i Pr, Cy, Ph), and acid chlorides . Although carbodiimides can act as versatile reagents for organic synthesis and organometallic chemistry, − the cleavage of chemical bonds in carbodiimide is relatively less explored in chemical transformations. − …”

Section: Resultsmentioning

confidence: 68%

Substituent-Controlled Selective Synthesis of N-Acyl 2-Aminothiazoles by Intramolecular Zwitterion-Mediated C–N Bond Cleavage

et al. 2014

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The cleavage of C-N bonds is an interesting and challenging subject in modern organic synthesis. We have achieved the first zwitterion-controlled C-N bond cleavage in the MCR reaction among lithium alkynethiolates, bulky carbodiimides, and acid chlorides to construct N-acyl 2-aminothiazoles. This is a simple, highly efficient, and general method for the preparation of N-acyl 2-aminothiazoles with a broad range of substituents. The selective synthesis of N-acyl 2-aminothiazoles significantly depends on the steric hindrance of carbodiimides. The result is in striking contrast with our previous convergent reaction giving 5-acyl-2-iminothiazolines via 1,5-acyl migration. It is indeed interesting that the slight change of the substituents on the carbodiimides can completely switch the product structure. Experimental and theoretical results demonstrate the reason why the C-N bond cleavage in the present system is prior to the acyl migration. The intramolecular hydrogen relay via unprecedented Hofmann-type elimination is essential for this totally new zwitterion-controlled C-N bond cleavage.

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“…This type of conversion, unknown in the literature, provides an efficient method of synthesis of 2-aminooxazoles. The title compound, (2), was obtained in 96% yield, which is much better than the known synthetic routes, where (2) has been synthesized either by the reaction of cyanourea with p-bromophenacyl bromide (Beiling et al, 1965;Beyer & Schilling, 1966;van Leusen et al, 1981) or by the Curtius rearrangement of the hydrazide of oxazolyl-2-carboxylic acid (Tanaka & Nishiki, 1967). We report here the crystal structure of (2).…”

Section: Commentmentioning

confidence: 94%