MAGNETIC RESONANCE IN CHEMISTRY Magn. Reson. Chem. 2007; 45: 87–89 Published online 2 November 2006 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/mrc.1918 Spectral Assignments and Reference Data Complete assignment of 1 H and 13 C NMR spectra of some a-arylthio and a-arylsulfonyl substituted N-methoxy-N-methyl propionamides Nelson L. C. Domingues, 1 Mirta G. Mondino, 2 Adriana K. C. A. Reis, 3 Roberto Rittner, 3 Filipe S. Lima 1 and Paulo R. Olivato 1 * 1 Conformational Analysis and Electronic Interactions Laboratory, Insti- tuto de Qu´ ımica, USP, Caixa Postal 26077, 05513-970 S ˜ ao Paulo, S ˜ ao Paulo, Brazil 2 F.C.F.B.-Faculdades Oswaldo Cruz, 01151-000, S ˜ ao Paulo, Brazil 3 Physical Organic Chemistry Laboratory, Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, S ˜ ao Paulo, Brazil Received 3 August 2006; revised 5 September 2006; accepted 29 September 2006 The complete assignments of the 1 H and 13 C NMR spectra of the some a-arylthio and a-arylsulfonyl substituted N-methoxy-N-methyl propionamides, bearing methoxy, methyl, chloro, and nitro as substituents at the phenyl ring are reported. Copyright  2006 John Wiley & Sons, Ltd. KEYWORDS: NMR; 1 H NMR; 13 C NMR; N-methyl propionamides INTRODUCTION N-methoxy-N-methylamides 1 (commonly named Weinreb amides) are important carboxylic acid derivatives that have been widely used for the preparation of ketones, whose synthetic utility has been extensively demonstrated. 2–4 The efficiency of the reaction involving these compounds has been attributed to the formation of an intermediate stable tetrahedral lithium chelate, 5 which precludes the second nucleophilic addition to the carbonyl group. This important characteristic of the chelate allowed us to synthesize some ketone derivatives of ˇ-lactams in good yields, which had not been possible through traditional methods employing other carboxylic acid derivatives. 6 The aim of this work was to prepare some 4 0 -substituted N-methoxy-N-methyl-2-phenylthio- and 4 0 -substituted N-methoxy- N-methyl-2-phenylsulfonyl-propionamides (Scheme 1) and to char- acterize them through their 1 H NMR and 13 C NMR spectra. EXPERIMENTAL Compounds The mild acylating agents 4 0 -substituted N-methoxy-N-methyl-2- phenylthio-propionamides are easy to prepare and are very stable for a long time. Initially, the 4 0 -substituted 2-phenylthiopropionic acids were obtained from the reaction of 2-bromopropionic acid with an aqueous solution of 4-substituted thiophenols and two equiva- lents of sodium hydroxide. 7 These acids were converted to the corresponding acyl chlorides, which led to the 4 0 -substituted N- methoxy-N-methyl-2-phenylthiopropionamides by their reaction with N,O-dimethylhydroxylamine hydrochloride. The obtained amides were oxidized to the corresponding sulfones using oxone [potassium peroxymonosulfate (2KHSO 5 . KHSO 4 .K 2 SO 4 )] in acetone solution and five equivalents of sodium L Correspondence to: Paulo R. Olivato, Instituto de Qu´ ımica – USP, Caixa Postal 26077, 05513-970 S˜ ao Paulo, SP, Brazil. E-mail: prolivat@iq.usp.br Y SO n H 3 C N OCH 3 CH 3 O 1 2 3 4 5 6 7 8 9 10 11 12 n = 0 n = 2 1 Y = MeO 6 Y = MeO 2 Y = Me 7 Y = Me 3 Y = H 8 Y = H 4 Y = Cl 9 Y = Cl 5 Y = NO 2 10 Y = NO 2 Scheme 1. Structures and numbering for compounds 1 – 10. bicarbonate. These compounds were obtained in 85–97% yield. Elemental analyses were carried out on a Perkin-Elmer 2400 CHN- standard analyzer (Table 1). Spectra 1 H NMR and 13 C NMR spectra were recorded on a Varian Inova 300 spectrometer (10% in CDCl 3 solutions) operating at 299.947 MHz and 75.423 MHz, respectively. Data processing was carried out on a Solaris workstation. 1 H NMR parameters were as follows: spectral width, 4000 Hz; data points, 32K, zero-filled to 64K; pulse width 45 ° , acquisition time, 4.10 s; digital resolution, 0.25 Hz. 13 C NMR parameters were as follows: spectral width, 18 860 Hz; data points, 64K, zero-filled to 128 K; pulse width 90 ° ; acquisition time, 1.76 s; digital resolution, 0.57 Hz, with a delay of 2.05 s between transients. 1 H and 13 C chemical shifts are given on the υ scale (ppm) and were referenced to TMS, and coupling constants J are reported in Hz. The following abbreviations were used: s, d, q and m, for singlet, doublet, quartet and multiplet, respectively. RESULTS AND DISCUSSION As a first step, the 1 H NMR spectra of compounds 3 and 8 (Y D H) were fully assigned and are in agreement with literature data. 8 The remaining compounds were then assigned by analogy. For compounds 1 – 10, the doublet signal at υ ¾ 1.4–1.6 ppm corresponds to the H-3 methyl group, attached to the chiral carbon (C-5), with a coupling constant of ¾7.0 Hz. (Table 2). The singlets at υ ¾ 3.2 ppm and υ ¾ 3.6–3.8 ppm correspond to H-1 and H-2 methyl groups, respectively, and the quartet at υ ¾ 4.1–4.8 ppm to the H-5 methine group, which has the chiral carbon (C-5). The low-frequency multiplet signals at υ 6.8–9.0 ppm were identified as the aromatic protons chemical shifts. The 13 C NMR chemical shifts are presented in Table 3. The signals at υ ¾ 32 ppm and at υ ¾ 61 ppm, for the whole series, correspond to C-1 and C-2, respectively. The deshielding for the chiral carbon C-5 (υ ¾ D 60 ppm) in compounds 6–10, in relation to 1–5 (υ ¾ D 41 ppm), may be ascribed to the larger inductive effect of the arylsulfonyl group ( I DC0.56), 9 in comparison to the arylthio group ( I DC0.31). 9 The inverse effect was observed for the C-3 methyl carbon attached to the chiral carbon and for the C-4 carbonyl carbon, where the corresponding shifts are deshielded in compounds 1–5 (υ ¾ D 17 ppm and υ ¾ D 173 ppm, respectively), in relation to 6–10 (υ ¾ D 13 ppm and υ ¾ D 166 ppm, respectively). The C-6 and C-9 aromatic carbons at υ ¾ 120–140 and υ ¾ 130–160 ppm, respectively, were largely dependent on the substituent in the aryl group, as expected, while less pronounced effects were observed for C-7/C-11 and C-8/C-10 chemical shifts, which are in agreement with reported values. 10 Copyright  2006 John Wiley & Sons, Ltd.