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Cooperative Effect of Carborane and Pyridine in the Reaction Of Cooperative effect of carborane and pyridine in the reaction of carboranyl alcohols with SOCl2 : halogenation versus oxidation Vincent Terrasson, Jose Giner Planas, Damien Prim, Clara Vinas, Francesc Teixidor, Mark E Light, Michael B Hursthouse To cite this version: Vincent Terrasson, Jose Giner Planas, Damien Prim, Clara Vinas, Francesc Teixidor, et al.. Coopera- tive effect of carborane and pyridine in the reaction of carboranyl alcohols with SOCl2 : halogenation versus oxidation. IMEBoron, 2008, Platja d’Aro, Spain. hal-02913342 HAL Id: hal-02913342 https://hal.archives-ouvertes.fr/hal-02913342 Submitted on 8 Aug 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Institut Lavoisier de Versailles Cooperative effect of carborane and pyridine in the reaction of UMR 8180 carboranyl alcohols with SOCl 2: halogenation versus oxidation. V. Terrasson, a,b J. G. Planas, a D. Prim, b C. Viñas, a F. Teixidor, a M.E. Light, c M.B. Hursthouse. c a Institut de Ciència de Materials de Barcelona (CSIC), Campus de la U.A.B, 08193 Bellaterra, Spain. bInstitut Lavoisier UMR CNRS 8180, Université de Versailles-Saint Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles, France. cSchool of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK. Organic chlorides are key compounds in organic synthesis since they serve as intermediates in a wide variety of reactions.[1] These molecules are commonly obtained by the reaction of an alcohol with thionyl chloride, one of the most employed halogenating reagents.[2] With the aim to synthesize new o-carborane derivatives for material science and catalytic applications, [3] we have prepared new carboranyl alcohols and carried out their reactions with thionyl chloride. If alcohols bearing a phenyl substituent gave the expected chlorinated compounds in good yields, those substituted with a pyridine ring surprisingly afforded the ketones as the only products under the same reaction conditions.[4] Figure 2 Following an adaptation to known procedures, [5] we have prepared the series of Chlorides 3 a-b and ketones 4 four new carboranyl methylalcohols bearing a phenyl 1a-b or a pyridine a-b have been unambiguously substituent 2a-b (Scheme 1). characterized by spectroscopic OH methods. Molecular structures Li 1a, R = Me, Ar = Ph, 95 % for 3a and 4a have been THF 1b, R = Ph, Ar = Ph, 90 % R + Ar-CHO Ar determined by X-ray structure -78 C, 1h R analysis (Figure 2). X-ray structure of 3a X-ray structure of 4a 2a, R = Me, Ar = 2-Pyridyl, 87 % Scheme 1 2b, R = Ph, Ar = 2-Pyridyl, 81 % Oxidation of the alcohols 2 a-b to the ketones 4 a-b is clearly affected by both These alcohols were obtained in good to excellent yields (Table 1) and fully the pyridine and carborane moities in the same molecule since either 1 a-b or the characterized by spectroscopic methods. organic counterpart (2-pyridyl)phenylmethanol 5 exclusively afford the chloride products (Schemes 2 and 4). Molecular structures for 1a and 2a have been determined by X-ray structure analysis (Figure 1). OH Cl Scheme 4 N N SOCl2 CH Cl 2 2 99 % 5 reflux, 16 h Figure 1 Scheme 5 The usual reaction pathway of ClOS the halogenation using SOCl 2 is O the formation of the intermediate X-ray structure of 1a X-ray structure of 2a SOCl2 ∆∆∆ 1a-b 3a-b C2B10H10 I. The latter affords the Whereas no intramolecular contacts are found in 1a, there is a clear intramolecular H corresponding chloride by a I nucleophilic addition of Cl - O-H…N hydrogen bond in 2a. Cl Nucleophilic Attack (Scheme 5). Reactions of the phenylmethylalcohol derivatives 1 a-b with an excess of SOCl 2 When the reaction of 2a with Scheme 6 under reflux conditions afforded the expected chlorides 3 a-b in excellent yields SOCl was monitored by NMR, (Scheme 2). 2 the complete conversion of the ClOS Cl OH alcohol to the intermediate II was O H observed within 5 min at room SOCl2 N ∆∆∆ SOCl2 2a-b 4a-b C2B10H10 R 3a, R = Me, 97 % temperature. rt R 3b, R = Ph, 90 % fast H CH2Cl2 Further transformation according 1 a-b reflux, 16 h II to Scheme 6 was only obtained Scheme 2 Proton Abstraction by heating the reaction medium. Base Surprisingly, the pyridylmethyl alcohols 2 a-b did not afford the expected chlorides under the same conditions but gave the ketones 4 a-b (Scheme 3). Halogenation versus oxidation in these compounds can be interpreted as a competition between nucleophilic addition of Cl - versus proton abstraction at O OH the benzylic position (Schemes 5 and 6). NMR data of the intermediate II N clearly show that the benzylic proton is more acidic than that for the starting N SOCl2 R 4a, R = Me, 88 % alcohol 2a (δ = 7.29 ppm compared to 5.11 ppm). This is probably due to the R CH2Cl2 4b, R = Ph, 91 % positive charge at the pyridine ring in II . This charge effect (making the 2 a-b reflux, 16 h benzylic proton more acidic) combined with the bulkiness of the carboranyl Scheme 3 fragment hindering the nucleophilic attack of Cl - could explain this unusual oxidation reaction. References [1] R. Bohlmann In Comprehensive Organic Synthesis ; B.M. Trost, I. Fleming, Eds.; Pergamon: Oxford, [4] V. Terrasson, J.G. Planas, D. Prim, C. Viñas, F. Teixidor, M.E. Light, M.B. Husrthouse, J. Org. 1991; Vol. 6, p 203. Chem. 2008 , accepted . [2] a) R.A. Moss, X. Fu, R.R. Sauers, J. Phys. Org. Chem. 2007 , 20 , 1. b) S.P. Marsden, Contemp. Org. [5] H. Nakamura, K. Aoyagi, Y. Yamamoto, J. Org. Chem. 1997 , 62 , 780. Synth. 1997 , 4, 118. [3] a) J.G. Planas, F. Teixidor, C. Viñas, M.E. Light, M.B. Hursthouse, Chem. Eur. J. 2007 , 13 , 2493. b) We thank CICYT (Project MAT2006-05339), Generalitat de Catalunya J.G. Planas, C. Viñas, F. Teixidor, M.E. Light, M.B. Hursthouse, CrystEngComm 2007 , 9, 888. c) V. (2005/SGR/00709), Spanish Government (RyC to J.G.P.), MENRT-France (grant to Terrasson, S. Marque, M. Georgy, J.-M. Campagne, D. Prim, Adv. Synth. Catal. 2006 , 348 , 2063. d) V. V.T.), CNRS, Université de Versailles and UK EPSRC for financial support. Terrasson, D. Prim, J. Marrot, Eur. J. Inorg. Chem. 2008 , 2739..
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