Research paperPiperidin-1-ylamidomethyltellurium derivatives: Synthesis and solid state structures
Graphical abstract
Introduction
The O-hydro-C-alkyl/aryl addition of Grignard reagents or organolithiums to aldehydes or ketones is an established method to prepare alcohols. Such reagents are however inaccessible in cases where the organic halide possesses a functional group. It is therefore not surprising that the C-bonded acyl, alkoxycarbonyl and amido (N-bonded as well) functionalized organometallic derivatives are known to only a limited extent. In the Reformatsky reaction, the addition of α-haloesters or α-halo N,N-disubstituted amides to an aldehyde or a ketone in the presence of zinc metal is believed to involve an organozinc compound, O=C(Y)CH2ZnBr (similar to RMgX) as an intermediate, albeit the alternative O-bonded structure CH2=C(Y)OZnBr cannot be ruled out on the basis of the X-ray diffraction data for the solid intermediate isolated in the reaction between t-BuOCOCH2Br and Zn [1].
The carbonyl activation of Csp3–X bond to insert elemental Te has been studied and practiced in our laboratory to obtain functionalized diorganotellurium diiodies from the organic iodides, YCOCH2I (Y = R, RO, NH2) [2], [3], [4]. This strategy has been successfully applied for the direct synthesis of the corresponding dibromides from α-bromo acylmethanes [5], but α-bromo alkoxycarbonylmethanes failed to react with tellurium powder when heated together up to about 100 °C [4]. Recently, the oxidative addition of α-bromo acetamides derived mainly from acyclic amines to elemental tellurium has been reported [6]. The structural diversity and broad range of pharmacological properties of natural and synthetic piperidine derivatives in general and N-acylpiperidine in particular [7], [8] prompted us to prepare tellurated N-acyl piperidines by a simple method and study (i) their reactions with aldehydes and ketones (cf. Reformatsky reagents) and (ii) change in the conformation of the heterocyclic ring upon telluration.
Section snippets
General procedures
Preparative work was performed under dry nitrogen. All solvents were purified and dried before use. α-Bromacetylpiperidine was prepared by slight modification in the literature method [9]. Bis(1-naphthyl)ditelluride, dimesitylditelluride and ditolylditelluride were prepared by reported methods [10], [11], [12]. Melting points were recorded in capillary tubes and are uncorrected. Microanalyses were carried out using a Carlo Erba 1108 analyzer. NMR spectra were recorded in CDCl3 on Bruker DRX300 (
Synthesis and spectra
α-Bromoacetylpiperidine adds oxidatively to tellurium powder under mild conditions to afford bis{(piperidin-1-yl)amidomethyl}tellurium dibromide (1b) and to aryltellurium(II) bromides (prepared in situ from the stoichiometric amounts of Br2 and diarylditellurides, ArTeTeAr) to give alkylaryltellurium dibromides, (C5H10NCOCH2)ArTeBr2 (Ar = 2,4,6-Me3C6H2, Mes, 2b; 1-C10H7, Nap, 3b; 4-MeC6H4, Tol, 4b (Scheme 1). While partial biphasic reduction of 1b with Na2S2O5 yields the symmetrical telluroether,
Conclusions
The piperidin-1-yl appended amidomethyl bromide adds readily to the low valent tellurium species to provide single-step syntheses of dialkyl- and alkylaryltellurium dibromides (1b–4b). The symmetrical telluroether, bis(piperidin-1-ylamidomethyl)telluride (1) is obtained by the reduction of the parent Te(IV) dibromide (1b) with aqueous sodium sulfite solution. However, the (piperidin-1-ylamidomethyl)aryltellurium bromides (2b–4b) are unstable in solution towards symmetrization and afford Ar2TeX2
Acknowledgments
SM is thankful to the Department of Science and Technology, Government of India, New Delhi, India for financial assistance under Women Scientists Fellowship Scheme (SR/WOS-A/CS-55/2012). The authors are thankful to the Director, C.D.R.I., Lucknow for 1H NMR and C, H analyses, at the Sophisticated Analytical Instrument Facility (SAIF). The authors also wish to acknowledge the assistance of Dr. Matthias Zeller in the collection of diffraction data for compound 1c and NSF Grant CHE 0087210, Ohio
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