Heteroaromatic benzyl ethers as intermediates for palladium-catalysed transfer hydrogenolysis of benzyl alcohols

a b s t r a c t 2-Allyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (ABIOD) has been studied by matrix-isolation infrared spectroscopy and quantum chemical calculations. A conformational search on the B3LYP/6-311++G(3df,3pd) potential energy surface of the molecule demonstrated the existence of three conformers, Sk, Sk 0 and C, with similar energies, differing in the orientation of the allyl group. The calculations predicted the Sk form as the most stable in the gaseous phase, whereas the Sk 0 and C conformers have calculated relative energies of ca. 0.6 and 0.8-3.0 kJ mol À1 , respectively (depending on the level of theory). In agreement with the relatively large (>6 kJ mol À1 ) calculated barriers for conformational interconversion, the three conformers could be efficiently trapped in an argon matrix at 10 K, the experimental infrared spectrum of the as-deposited matrix fitting well the simulated spectrum built from the calculated spectra for individual conformers scaled by their predicted populations at the temperature of the vapour of the compound prior to matrix deposition. Upon annealing the matrix at 24 K, however, both Sk and Sk 0 conformers were found to convert to the more polar C conformer, indicating that this latter form becomes the most stable ABIOD conformer in the argon matrix.

Section: Introductionmentioning

confidence: 99%

Conformational and structural analysis of 2-allyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide as probed by matrix-isolation spectroscopy and quantum chemical calculations

Gómez‐Zavaglia

Kaczor

Coelho

et al. 2009

“…Apart from the wide commercial applications of saccharin itself, its derivatives receive an increased attention as they show herbicidal [1,2], antimicrobial and antifungal activity [3][4][5] or potential in enzymatic inhibition [6]. Additionally, substituted 1,2-benzisothiazole 1,1-dioxides (pseudosaccharins) are important intermediates in the organic synthesis, as their O-ethers provide efficient intermediates for reductive cleavage of the CAO bond in phenols [7,8], benzylic [9] and naphthylmethylic alcohols [10], through heterogeneous catalytic transfer hydrogenolysis, or through cross-coupling with organometalic reagents [11][12][13]. Though substituent is an additional requirement, ensuring a proper alignment of the compound on a catalyst surface (alkylpseudosaccharyl ethers are unreactive) [8], the structural basis of the enhanced reactivity of this kind of pseudosaccharyl ethers towards transition metal-catalyzed ipso-replacement lies in the unusual bond lengths and geometry of their C R AOAC A linkage (where R = heteroaromatic ring and A = aliphatic or aryl group) [8][9][10][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, substituted 1,2-benzisothiazole 1,1-dioxides (pseudosaccharins) are important intermediates in the organic synthesis, as their O-ethers provide efficient intermediates for reductive cleavage of the CAO bond in phenols [7,8], benzylic [9] and naphthylmethylic alcohols [10], through heterogeneous catalytic transfer hydrogenolysis, or through cross-coupling with organometalic reagents [11][12][13]. Though substituent is an additional requirement, ensuring a proper alignment of the compound on a catalyst surface (alkylpseudosaccharyl ethers are unreactive) [8], the structural basis of the enhanced reactivity of this kind of pseudosaccharyl ethers towards transition metal-catalyzed ipso-replacement lies in the unusual bond lengths and geometry of their C R AOAC A linkage (where R = heteroaromatic ring and A = aliphatic or aryl group) [8][9][10][13][14][15][16][17][18]. The strong electron withdrawing effect of the pseudosaccharyl group results in significant lengthening of the C A AO bond at the expense of the C R AO bond, which then gains partial double-bond character [8][9][10]13,19].…”

Section: Introductionmentioning

confidence: 99%

Molecular structure and infrared spectra of the monomeric 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (methyl pseudosaccharyl ether)

Kaczor

Almeida

Gómez‐Zavaglia

et al. 2008

The computational description of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide) and its derivatives is difficult due to the presence of hypervalent S@O bonds in their structures. Therefore, in this investigation, the HF, DFT/B3LYP and MP2 methods were used to predict the geometry and the infrared spectrum of the saccharyl derivative 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (MBID). Their relative predictive capabilities were then evaluated by comparing the obtained results with experimentally available data, namely the newly obtained IR spectra of MBID isolated in low-temperature inert matrices. For each method, different basis sets [6-31++G(d,p), 6-31++G(3df,3pd), 6-311++G(d,p), 6-311++G(2df,2pd), 6-311++G(3df,3pd), aug-cc-pVDZ and aug-cc-pVTZ] were considered. The best overall agreement has been achieved at the B3LYP/6-311++G(3df,3pd) and B3LYP/6-31++G(3df,3pd) levels of theory, showing the adequacy of the B3LYP functional to describe the investigated properties in this type of compounds and stressing the relevance of including high-order polarization functions in the basis set.The chosen level of theory 3pd)] was applied to analyze the vibrational spectra and the geometry of the title molecule. In agreement with the experiment, the CAOAC linkage in MBID is predicted by these calculations to exhibit considerably short (1.320 Å ) and long (1.442 Å ) (N@)CAO and (H 3 )CAO bonds, respectively, and a hybridization of the central oxygen atom close to sp 2 (the CAOAC angle is predicted to be ca. 117°). This CAOAC bonding pattern fits the well-known high reactivity of MBID upon thermal rearrangement, which has been shown to result in easy selective [1,3 0 ]-isomerization of the compound.

Section: Introductionmentioning

confidence: 99%

“…Due to the powerful electron-withdrawing properties of the saccharyl system, benzisothiazolyl ethers have been successfully used as intermediate compounds for reductive cleavage of C-O bonds in phenols, benzyl-and naphthyl alcohols, catalysed by transition metals, using hydrogen donors [2][3][4]. The saccharyl system, together with the oxygen from the original phenol or alcohol, represents an efficient nucleofuge in heterogeneous catalytic transfer hydrogenolysis [2][3][4] or cross-coupling with organometallic reagents [5]. The electron-withdrawing abilities of the benzisothiazolyl system are also in keeping with the easy thermally induced sigmatropic isomerisation of 3-allyloxy-and 3-alkoxy-derivatives of benzisothiazole to the corresponding N-allyl or N-alkyl isomers [6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Matrix-isolation FTIR, theoretical structural analysis and reactivity of amino-saccharins: N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N-methyl amine and -N,N-dimethyl amine

Almeida¹,

Gómez‐Zavaglia²,

Kaczor³

et al. 2009

a b s t r a c tIn this work, two novel amino-substituted derivatives of saccharin, N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N-methyl amine (MBAD) and N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-N,N-dimethyl amine (DMBAD), were synthesized and characterized, and their molecular structure and vibrational properties were investigated by matrix-isolation FTIR spectroscopy and theoretical calculations undertaken using different levels of approximation. The calculations predicted the existence of two conformers of MBAD. The lowest energy form was predicted to be considerably more stable than the second conformer (DE > ca. 20 kJ mol À1) and was the sole form contributing to the infrared spectrum of the compound isolated in solid xenon. Both conformers have planar amine moieties. In the case of DMBAD, only one doubly-degenerated-by-symmetry conformer exists, with the amine nitrogen atom considerably pyramidalized. The effect of the electron-withdrawing saccharyl ring on the C-N bond lengths is discussed. The different structural preferences around the amine nitrogen atom in the two molecules were explained in terms of repulsive interactions involving the additional methyl group of DMBAD. Observed structural features are correlated with the reactivity exhibited by the two compounds towards nucleophiles. The experimentally obtained spectra of the matrix-isolated monomers of MBAD and DMBAD were fully assigned by comparison with the corresponding calculated spectra.