- The photodecomposition mechanism of tert-butyl-9-methylfluorene-9- percarboxylate: New insight from femtosecond IR spectroscopy
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The ultrafast photodissociation of tert-butyl-9-methylfluorene-9- percarboxylate (TBFC) is studied by mid-infrared transient absorption spectroscopy after UV excitation at 266 nm. By means of 13C-labeled TBFC and additional DFT calculations transient IR bands in the fingerprint region were unambiguously assigned to the methylfluorenyl radical. The experiments show that the fragmentation is controlled by the S 1-lifetime of TBFC and, dependent on the solvent, within 0.8-2.1 ps leads to tert-butyloxy and methylfluorenyl radicals plus CO2via concerted bond breakage of the O-O and the fluorenyl-C(carbonyl) bond. In accordance, the CO2 quantum yield is determined to be unity.
- Reichardt, Christian,Schroeder, Joerg,Schwarzer, Dirk
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- SYSTEM PROVIDING CONTROLLED DELIVERY OF GASEOUS CO FOR CARBONYLATION REACTIONS
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A carbonylation system comprising at least one carbon monoxide producing chamber and at least one carbon monoxide consuming chamber forming an interconnected multi-chamber system, said interconnection allowing carbon monoxide to pass from the at least one carbon monoxide producing chamber to the at least one carbon monoxide consuming chamber, said at least one carbon monoxide producing chamber containing a reaction mixture comprising a carbon monoxide precursor and a catalyst, said at least one carbon monoxide consuming chamber being suitable for carbonylation reactions, said interconnected multi- chamber system being sealable from the surrounding atmosphere during carbonylation.
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Page/Page column 86
(2012/06/30)
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- 14Carbon monoxide made simple - Novel approach to the generation, utilization, and scrubbing of 14carbon monoxide
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A new method is reported for the efficient generation of 14CO that can be applied in transition metal-catalyzed carbonylation reactions. 14CO is produced by palladium-catalyzed decarbonylation of the stable acid chloride, 14COgen. When combined in a two-chamber system, the produced 14CO is incorporated into the target molecule with high efficiency. As the carbonylation chemistry is performed under mild conditions, this allows the 14C isotope to enter the synthesis into an advanced stage intermediate. The presented work includes two aminocarbonylations, one amidocarbonylation, and one carbonylative Suzuki-Miyaura coupling, all installing the 14C isotope in the final step of the synthesis. Finally, the identification of a highly efficient scrubber for the safe trapping and removal of any leftover 14CO is also disclosed. A new method for the simple generation of 14CO from a stable, easy to handle CO precursor 14COgen is presented. When combined with a two-chamber system, COware, the generated 14CO is successfully applied as the limiting reagent in any carbonylation reaction. Owing to the mild conditions, the desired labeled compounds could be obtained in the final synthetic step of a linear synthesis. Finally, the development of a highly efficient scrubber, capable of removing any remaining or excess 14CO, is presented. This method provides radiochemists with a complete solution for performing 14C-carbonylation chemistry. Copyright
- Lindhardt, Anders T.,Simonssen, Roger,Taaning, Rolf H.,Gogsig, Thomas M.,Nilsson, Goeran N.,Stenhagen, Gunnar,Elmore, Charles S.,Skrydstrup, Troels
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p. 411 - 418
(2013/01/15)
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- Ex situ generation of stoichiometric and substoichiometric 12CO and 13CO and its efficient incorporation in palladium catalyzed aminocarbonylations
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A new technique for the ex situ generation of carbon monoxide (CO) and its efficient incorporation in palladium catalyzed carbonylation reactions was achieved using a simple sealed two-chamber system. The ex situ generation of CO was derived by a palladium catalyzed decarbonylation of tertiary acid chlorides using a catalyst originating from Pd(dba)2 and P(tBu)3. Preliminary studies using pivaloyl chloride as the CO-precursor provided an alternative approach for the aminocarbonylation of 2-pyridyl tosylate derivatives using only 1.5 equiv of CO. Further design of the acid chloride CO-precursor led to the development of a new solid, stable, and easy to handle source of CO for chemical transformations. The synthesis of this CO-precursor also provided an entry point for the late installment of an isotopically carbon-labeled acid chloride for the subsequent release of gaseous [ 13C]CO. In combination with studies aimed toward application of CO as the limiting reagent, this method provided highly efficient palladium catalyzed aminocarbonylations with CO-incorporations up to 96%. The ex situ generated CO and the two-chamber system were tested in the synthesis of several compounds of pharmaceutical interest and all of them were labeled as their [ 13C]carbonyl counterparts in good to excellent yields based on limiting CO. Finally, palladium catalyzed decarbonylation at room temperature also allowed for a successful double carbonylation. This new protocol provides a facile and clean source of gaseous CO, which is safely handled and stored. Furthermore, since the CO is generated ex situ, excellent functional group tolerance is secured in the carbonylation chamber. Finally, CO is only generated and released in minute amounts, hence, eliminating the need for specialized equipment such as CO-detectors and equipment for running high pressure reactions.
- Hermange, Philippe,Lindhardt, Anders T.,Taaning, Rolf H.,Bjerglund, Klaus,Lupp, Daniel,Skrydstrup, Troels
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supporting information; experimental part
p. 6061 - 6071
(2011/06/19)
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