Reaction of N -benzyl azomethine ylide with aryl isothiocyanates: synthesis of ( Z )- N -aryl-3-benzylthiazolidine-5-imi
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Reaction of N-benzyl azomethine ylide with aryl isothiocyanates: synthesis of (Z)-N-aryl-3-benzylthiazolidine-5-imines Evgeny M. Buev1*, Anna P. Osintseva1, Vladimir S. Moshkin1, Vyacheslav Ya. Sosnovskikh1 1
Institute of Natural Sciences and Mathematics, Ural Federal University named after the first President of Russia B. N. Yeltsin, 51 Lenina Ave., Yekaterinburg 620000, Russia; е-mail: [email protected]
Translated from Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(9), 1222–1225
Submitted February 20, 2020 Accepted March 23, 2020
The reaction of aryl isothiocyanates with nonstabilized azomethine ylides generated in situ by various methods was studied. It was established that the use of N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine in the presence of trifluoroacetic acid in the role of a catalyst led to the formation of (Z)-N-aryl-3-benzylthiazolidin-5-imines in 22–47% yields. Keywords: azomethine ylides, isothiocyanates, thiazolidines, [3+2] cycloaddition.
Nonstabilized azomethine ylides are commonly employed by organic chemists for the synthesis of various nitrogen heterocycles via [3+2] cycloaddition reactions to activated alkenes.1 Recently, there has been a growing interest by researchers toward using the cycloaddition reactions of azomethine ylides to heterodipolarophiles C = X (where X = N, O, S), leading to the formation of imidazolidines, oxazolidines, and thiazolidines.2 For this reason, it is important to characterize the chemoselectivity of such reactions when the starting dipolarophile contains two different double bonds. For example, it was found that 1,3-dipolar cycloaddition proceeded more readily at an activated С=С double bond compared to a С=О bond.3 We recently studied spiro[anthracene-9,5'-oxazolidine] 2 as a precursor of azomethine ylides А in reactions with aroyl azides 1, which underwent a Curtius rearrangement upon heating in a microwave reactor and in situ formed aryl isocyanates 3 that reacted with azomethine ylide А present in the reaction medium (Scheme 1).4 As a result, imidazolidin-4-ones 4 were isolated as products of ylide addition at the С=N bond, while adducts at the С=О bond were not detected. Unsubstituted phenyl isocyanate reacted analogously. In a continuation of that work, we were interested in any changes in the selectivity of this reaction as a result of replacing the oxygen atom in the molecule of isocyanate 3 0009-3122/20/56(9)-1222©2020 Springer Science+Business Media, LLC
Scheme 1
with a sulfur atom. Taking into account the fact that the cycloaddition reaction of azomethine ylides with thiones proceeds easier than with ketones,2a one could expect the formation of both imidazolidines 6 (adducts at the С=N bond) and thiazolidines 7 (adducts at the С=S bond) upon the use of isothiocyanates5 5 (Scheme 2). The reactions of isothiocyanates 5 with nonstabilized azomethine ylides have not been previously studied. Scheme 2
1222
S Ar
N R
N 6
S H2C– C + N R N H2C Ar 5 A
S Ar
N
7
N R
Chemistry of Heterocyclic Compounds 2020, 56(9), 1222–1225
At the s
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