- Investigation of the Deprotonative Generation and Borylation of Diamine-Ligated α-Lithiated Carbamates and Benzoates by in Situ IR spectroscopy
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Diamine-mediated α-deprotonation of O-alkyl carbamates or benzoates with alkyllithium reagents, trapping of the carbanion with organoboron compounds, and 1,2-metalate rearrangement of the resulting boronate complex are the primary steps by which organoboron compounds can be stereoselectively homologated. Although the final step can be easily monitored by 11B NMR spectroscopy, the first two steps, which are typically carried out at cryogenic temperatures, are less well understood owing to the requirement for specialized analytical techniques. Investigation of these steps by in situ IR spectroscopy has provided invaluable data for optimizing the homologation reactions of organoboron compounds. Although the deprotonation of benzoates in noncoordinating solvents is faster than that in ethereal solvents, the deprotonation of carbamates shows the opposite trend, a difference that has its origin in the propensity of carbamates to form inactive parasitic complexes with the diamine-ligated alkyllithium reagent. Borylation of bulky diamine-ligated lithiated species in toluene is extremely slow, owing to the requirement for initial complexation of the oxygen atoms of the diol ligand on boron with the lithium ion prior to boron-lithium exchange. However, ethereal solvent, or very small amounts of THF, facilitate precomplexation through initial displacement of the bulky diamines coordinated to the lithium ion. Comparison of the carbonyl stretching frequencies of boronates derived from pinacol boronic esters with those derived from trialkylboranes suggests that the displaced lithium ion is residing on the pinacol oxygen atoms and the benzoate/carbamate carbonyl group, respectively, explaining, at least in part, the faster 1,2-metalate rearrangements of boronates derived from the trialkylboranes.
- Mykura, Rory C.,Veth, Simon,Varela, Ana,Dewis, Lydia,Farndon, Joshua J.,Myers, Eddie L.,Aggarwal, Varinder K.
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supporting information
p. 14677 - 14686
(2018/11/20)
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- Isotopically enriched 13C diffusion-ordered NMR spectroscopy: Analysis of methyllithium
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We report the development of isotopic-labeled 13C diffusion-ordered NMR spectroscopy (DOSY) NMR with diffusion coefficient-formula weight (D-FW) analysis and its application in characterizing the aggregation state of methyllithium aggregates and complexes with several widely used diamines. Commercially available 13C-labeled benzene and several easily synthesized 13C-labeled compounds using 13C-labeled iodomethane as the isotopic source are developed as internal references for diffusion-formula weight analysis (D-FW). The technique greatly expands the applicability of DOSY D-FW analysis to a much wider variety of compounds because of isotopic labeling. These results reveal that methyllithium exists as a tetrasolvated tetramer in diethyl ether and exclusively as bis-solvated dimers with chelating diamines.
- Su, Chicheung,Hopson, Russell,Williard, Paul G.
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p. 11733 - 11746
(2014/01/06)
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- Microwave-assisted Raney nickel reduction of bispidinone thioketals to N,N′-dialkylbispidines
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A series of N,N′-dialkyl-3,7-diazabicyclo[3.3.1]nonanes was prepared by microwave-assisted reduction of a common dithiolane precursor with Raney nickel, using the corresponding alkanol as solvent. The method avoids the use of hydrazine. Georg Thieme Verla
- Toom, Lauri,Grennberg, Helena,Gogoll, Adolf
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p. 2064 - 2068
(2007/10/03)
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- Guest/host relationships in the synthesis of the novel cage-based zeolites SSZ-35, SSZ-36, and SSZ-39
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Here, we report the synthesis and structure of three high-silica molecular sieves, SSZ-35, SSZ-36, and SSZ-39, that are prepared from a library of 37 different cyclic and polycyclic quaternized amine molecules that are used as structure-directing agents (SDAs). The size and shape of the quaternized amine molecules are purposely designed in order to obtain novel zeolite structures, and the synthesis of these molecules is presented. The selectivity for the three molecular sieve phases is found to depend on both the SDA and the degree of heteroatom lattice substitution of Al3+ or B3+ in the silicate framework. Molecular modeling is utilized to probe the effects of the nonbonded SDA/zeolite-framework interaction energy on the selectivity for the observed molecular sieve phase. The Rietveld refinement of the powder X-ray data confirms the structure of the SSZ-39 zeolite to be isomorphous with the aluminophosphate molecular sieve, SAPO-18 (AEI). The structure of SSZ-36 is found to possess a range of fault probabilities between the two-dimensional channel system, end-member polymorphs, ITQ-3 and RUB-13 (International Zeolite Association Codes ITE and RTH, respectively). The SSZ-35 structure is reported to contain a one-dimensional pore system possessing stacked cages circumscribed by alternating rings of 10 and 18 tetrahedral atoms (10- and 18-membered rings).
- Wagner, Paul,Nakagawa, Yumi,Lee, Greg S.,Davis, Mark E.,Elomari, Saleh,Medrud, Ronald C.,Zones
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p. 263 - 273
(2007/10/03)
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