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Selected Publications

  1. "Camphorquinone: A new and efficient oxidant for the preparation of 2-thio-substituted benzothiazoles from alcohols by oxidation-reduction condensation." Pluempanupat, W.; Temyarasilp, P.; Widhalm, M.; Chavasiri, W.  J. Sulfur Chem. 2014, 35, 418–430. PDF

    A convenient one-pot procedure for the preparation of various 2-thio-substituted benzothiazoles from alcohols and benzothiazole-2-thiol utilizing camphorquinone-mediated oxidation-reduction condensation is disclosed. The condensation between benzothiazole-2-thiol and alkyl diphenylphosphinites, generated in situ from alcohols and chlorodiphenylphosphine, proceeded smoothly in the presence of camphorquinone to furnish the corresponding benzothiazoles in good to moderate yields.
  2. "Tandem RCM–Claisen Rearrangement–[2+2] Cycloaddition of O,O'-(But-2-en-1,4-diyl)-bridged Binaphthols" Abraham, M.; Reischl, W.; Kirchner, K. A.; Roller, A.; Veiros, L.F.; Widhalm, M. Molecules 2012, 17, 14531–14554. PDF

    Attempted RCM of 2,2'-bis(allyloxy)-1,1'-binaphthyl resulted in a Claisen-type rearrangement of a postulated labile dioxacyclodecine proceeding at room temperature and followed by [2+2] cycloaddition. Structures of products were confirmed by X-ray crystallography. A mechanistic rationalisation based on relative stabilities of proposed transition states is provided.
  3. "Regio- and Stereoselective Approach to 1,4-Di-tert. Carbinols from Dimethyl Tartrate" Budragchaa, T.; Roller, A.; Widhalm, M. Synthesis 2012, 3238–3250. PDF

    A rational strategy for accessing tetrahydroxy compounds in predictable stereoselective fashion from di-O-benzyl protected tartrate is presented. Up to four different aromatic, aliphatic and vinyl substituents could be stepwise introduced at C1 and C4. This is exemplified in an economic preparation of eight dihydroxy compounds from natural tartaric acid in six steps and 19–59% overall yield. A final deprotection step afforded the corresponding tetrahydroxy compounds in good yield.
  4. "Synthesis and Conformation of Chiral Biheteroaryls" Pluempanupat,  W.; Abraham, M.; Brecker, L.; Wolschann, P.; Karpfen, A.; Arion, V. B.; Widhalm, M. J. Org. Chem. 2011, 76, 3222–3230. PDF

    Bridging 2,3 and 2’,3’ positions in 2,2’-dihydroxy-1,1’-binaphthyl and 2,2’-diamino-1,1’-binaphthyl, respectively  resulted in formation of chiral O- and N-bis-tricyclic compounds accessible in 4 steps from known 3,3’-diiodo precursors. In both cases, two-fold ring closing metathesis of tetra-allyl intermediates proceeded regioselectively to give tetrahydro-binaphtho[2,3-b]oxepine and –azepine, respectively. In case of the N-mesyl-N-allyl precursor, three, at room temperature separable, rotamers were isolated and characterized by NMR spectroscopy and X-ray structure determination. Their interconversion (process I) was followed by NMR, yielding rate constants and thermodynamic parameters. The two predominating rotamers with either C1 or C2 symmetry were stereospecifically cyclized to conformatively moderately stable bis-sulfonamides. Also in this case, the kinetics of their interconversion (process II) was investigated and from two of them the crystal structure was determined. Processes I and II were investigated by a DFT method, M06-2X, to gain insight into electronic and steric peculiarities responsible for the remarkable conformative stabilities. Transition state geometries and energies were calculated and compared with empirical data.
  5. "A modular approach to a new class of phosphinohydrazones and their use in asymmetric allylic alkylation reactions" Widhalm, M.; Abraham, M.; Arion, V. B.; Saarsalu, S.; Maeorg, U. Tetrahedron: Asymmetry 2010, 21, 1971–1982. PDF

    A group of five phosphino hydrazones with pendant binaphthyl unit as chiral modifyer have been synthesized from non-racemic 2,2’-bis(bromomethyl)-1,1’-binaphthyl and 3,3’-diiodo-2,2’-bis(bromomethyl)-1,1’-binaphthyl as the key intermediates. Their efficiency as chiral ligands in palladium catalyzed allylic alkylation reactions has been investigated showing up to 95% e.e. under optimized conditions. X-ray diffraction structures of mono- and dimeric Pd complexes are reported.
  6. "A new route to 2,2',3,3'-tetrasubstituted binaphthyls" Widhalm, M.; Aichinger, C.; Mereiter, K. Tetrahedron Lett. 2009, 50, 2425–2429. PDF

    Based on an ortho-lithiation protocol of 2,2'-dibromo-1,1'-binaphthyl four tetrasubstituted binaphthyls, 2,2'-dibromo-3,3'-diiodo-, 3,3'-dibromo-2,2'-diiodo-, as well as 2,2',3,3'-tetrabromo-, and 2,2',3,3'-tetraiodo-1,1'-binaphthyl have been prepared in excellent yield which in turn proved to be versatile key intermediates in the synthesis of various 2,2',3,3'-tetrasubstituted 1,1'-binaphthyl derivatives.
  7. "An expedient synthesis of dialkyl phosphine borane complexes from sodium phosphide, and their alkylation under phase transfer conditions" Kasák, P.; Widhalm, M. Synthesis 2007, 2987–2994. PDF

    A group of seven achiral, α- and β-chiral dialkylphosphanes were synthesized in one step from sodium phosphide and alkyl sulfonates or sulfates. The corresponding borane complexes were further alkylated with alkyl, allyl and benzyl bromides and mesylates to give tertiary mono- and diphosphanes, either via lithio phosphide borane complexes at low temperature (45-78%) or under phase transfer conditions (79-91%).
  8. "(R,R,R)-Tris(2-hydroxy-1-methylethyl)- and (S,S,S)-tris(2-hydroxy-2-methylethyl)phosphine. Watersoluble chiral trialkylphosphines with C3-symmetry" Kasák, P.; Arion, V. B.; Widhalm, M. Tetrahedron Lett. 2007, 48, 5665–5668. PDF

    The first α- and β-chiral water-soluble trialkylmonophosphines, 1 and 2, respectively, both with C3 symmetry, were synthesised from sodium phosphide and chiral mesylates, accessible from (S)-ethyl lactate. X-ray structures of a corresponding 2:1 gold(I) complex [12Au(I)]OTf and of a borane complex 2⋅BH3 were determined.
  9. "A chiral phosphepine-olefin rhodium complex as an efficient catalyst for the asymmetric conjugate addition" Kasák, P.; Arion, V. B.; Widhalm, M. Tetrahedron: Asymmetry 2006, 17, 3084–3090. PDF

    A monophosphine-olefin was synthesized from a 2,2’-bridged 1,1’-binaphthyl precursor which served as a chiral bidentate ligand in Rh catalyzed 1,4-additions of arylboronic acids to cycloalkenones and 5,6-dihydro-2H-pyran-2-one. Fair yields (64-88%) and high asymmetric inductions (88-98%e.e.) have been obtained. The crystal structure of a corresponding cationic Rh(I) complex was determined.
  10. "Rigid P-chiral mono and diphosphines. Configurative stability and P-inversion barrier" Widhalm, M.; Brecker, L.; Mereiter, K. Tetrahedron: Asymmetry 2006, 17, 1355–1369. PDF

    A group of P-chiral monophosphine oxides and one diaryl diphosphine oxide based on the dibenzophosphole skeleton are synthesized. Preparative enantioselective chromatography of 4-trimethylsilyl-5-phenyl-5H-dibenzophosphol oxide followed by simple transformation with exchange of substituents (and a homo-coupling reaction in one case) and a stereoselective reduction step furnished corresponding phosphines in fair to good yield. Their relative and absolute configurations were determined by crystal structure analysis. It turned out that racemisation of phosphines through P-inversion takes place at ambient temperature and depends markedly on ortho substituents (104-114 kJ mol-1). In case of the diphosphine racemisation can be suppressed when forming a chelate in Pd(II) or Ni(II) complexes.
  11. "Chiral α-branched mono phosphine auxiliaries, reversal of sense of asymmetric induction upon Substitution." Kasák, P.; Mereiter, K.; Widhalm, M. Tetrahedron: Asymmetry 2005, 16, 3416–3426. PDF

    A group of ten (mono- or bis-) α-chiral mono phosphine ligands L was synthesized from enantiopure phosphepine sulfide by one or two subsequent, highly diastereoselective –deprotonation / alkylation steps, followed by desulfuration with Raney nickel. Their relative configuration was determined by crystal structure analysis. The new monophosphine ligands were tested in asymmetric hydrogenation, hydroboration, and Suzuki-Miyaura coupling showing asymmetric induction up to 91% e.e. In the case of hydrogenation clear evidence was found that enantiodifferentiation is substantially controlled through α–C chirality rather than through biaryl chirality which is evidently demonstrated by a change of the sense of asymmetric induction upon substitution of ligands.
  12. "Metallation Reactions on 2,2'-Bis(diphenylphosphinoyl)-1,1'-binaphthyl [BINAP(O)2]" Widhalm, M.; Mereiter, K. Bull. Chem. Soc. Jpn. 2003, 76, 1233–1244. PDF

    The behavior of BINAP(O)2 upon treatment with lithium or magnesium amides at various conditions has been studied. The reaction with N-(2,2,6,6-tetramethylpiperidino)magnesium bromide resulted in selective metallation of ortho positions of opposed phenyl rings thereupon forming stable intermediates, while the use of lithium amides caused rearrangements with displacement of one diphenylphosphinoyl group and the formation of strained P-heterocycles. Monophosphine oxides have been reduced to phosphines in good yield, while substituted BINAP(O)2 derivatives failed to give the desired diphosphines. Crystal structures of six phosphine oxides and one phosphine have been determined.

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