Cycloreversion of beta-lactams via photoinduced electron transfer

The radical anions of beta-lactams, photogenerated in the presence of DABCO as an electron donor, undergo cycloreversion via N-C4 bond cleavage, back electron transfer and final C2-C3 bond cleavage, leading to olefins. The involved intermediates are 1,4-radical anions and 1,4-biradicals. The experimental observations are consistent with the results of DFT calculations.Financial support from the Spanish Government (CTQ2013-47872-C2-1-P, SEV-2012-0267, BES-2011-043706, JCI-2010-06204), from CSIC (JAEDOC 101-2011 co-funded by FSE) and from the Generalitat Valenciana (PROMETEOII/2013/005) is gratefully acknowledged. J. A. S. acknowledges the computational facilities provided by the Theoretical Computational Chemistry Group of Prof. L. R. Domingo at the Universitat de Valencia.Pérez Ruiz, R.; Sáez Cases, JA.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2014). Cycloreversion of beta-lactams via photoinduced electron transfer. Organic and Biomolecular Chemistry. 12(42):8428-8432. https://doi.org/10.1039/c4ob01416bS842884321242Von Nussbaum, F., Brands, M., Hinzen, B., Weigand, S., & Häbich, D. (2006). Antibacterial Natural Products in Medicinal Chemistry—Exodus or Revival? Angewandte Chemie International Edition, 45(31), 5072-5129. doi:10.1002/anie.200600350β-Lactams in the New Millennium. Part-I: Monobactams and Carbapenems. (2004). Mini-Reviews in Medicinal Chemistry, 4(1), 69-92. doi:10.2174/1389557043487501β-Lactams in the New Millennium. Part-II: Cephems, Oxacephems, Penams and Sulbactam. (2004). Mini-Reviews in Medicinal Chemistry, 4(1), 93-109. doi:10.2174/1389557043487547Buynak, J. (2004). The Discovery and Development of Modified Penicillin- and Cephalosporin- Derived β-Lactamase Inhibitors. Current Medicinal Chemistry, 11(14), 1951-1964. doi:10.2174/0929867043364847Veinberg, G., Vorona, M., Shestakova, I., Kanepe, I., & Lukevics, E. (2003). Design of β-Lactams with Mechanism Based Nonantibacterial Activities. Current Medicinal Chemistry, 10(17), 1741-1757. doi:10.2174/0929867033457089Chemistry and Biology of β-Lactam Antibiotics , ed. R. B. Morin and M. Gorman , Academic Press , New York , 1982 , pp. 1–3Nathwani, D., & Wood, M. J. (1993). Penicillins. Drugs, 45(6), 866-894. doi:10.2165/00003495-199345060-00002Fischer, M. (1968). Photochemische Reaktionen, IV. Photochemische Fragmentierungen von β-Lactamen. Chemische Berichte, 101(8), 2669-2678. doi:10.1002/cber.19681010809Fabre, H., Ibork, H., & Lerner, D. A. (1994). Photoisomerization Kinetics of Cefuroxime Axetil and Related Compounds. Journal of Pharmaceutical Sciences, 83(4), 553-558. doi:10.1002/jps.2600830422Rossi, E., Abbiati, G., & Pini, E. (1999). Substituted 1-benzyl-4-(benzylidenimino)-4-phenylazetidin-2-ones: Synthesis, thermal and photochemical reactions. Tetrahedron, 55(22), 6961-6970. doi:10.1016/s0040-4020(99)00325-7Gómez-Gallego, M., Alcázar, R., Ramírez, P., Vincente, R., J. Mancheño, M., & A. Sierra, M. (2001). A Study of the Photochemical Isomerization in b-Lactam Rings. HETEROCYCLES, 55(3), 511. doi:10.3987/com-00-9127MUKERJEE, A. K., & SINGH, A. K. (1975). Reactions of Natural and Synthetic β-Lactams. Synthesis, 1975(09), 547-589. doi:10.1055/s-1975-23842Mukerjee, A. K., & Singh, A. K. (1978). β-Lactams: retrospect and prospect. Tetrahedron, 34(12), 1731-1767. doi:10.1016/0040-4020(78)80209-9Pérez-Ruiz, R., Jiménez, M. C., & Miranda, M. A. (2014). Hetero-cycloreversions Mediated by Photoinduced Electron Transfer. Accounts of Chemical Research, 47(4), 1359-1368. doi:10.1021/ar4003224Pérez-Ruiz, R., Sáez, J. A., Domingo, L. R., Jiménez, M. C., & Miranda, M. A. (2012). Ring splitting of azetidin-2-ones via radical anions. Organic & Biomolecular Chemistry, 10(39), 7928. doi:10.1039/c2ob26528aRehm, D., & Weller, A. (1970). Kinetics of Fluorescence Quenching by Electron and H-Atom Transfer. Israel Journal of Chemistry, 8(2), 259-271. doi:10.1002/ijch.197000029Kavarnos, G. J., & Turro, N. J. (1986). Photosensitization by reversible electron transfer: theories, experimental evidence, and examples. Chemical Reviews, 86(2), 401-449. doi:10.1021/cr00072a005Gandon, V., Bertus, P., & Szymoniak, J. (2000). A Straightforward Synthesis of Cyclopropanes from Aldehydes and Ketones. European Journal of Organic Chemistry, 2000(22), 3713-3719. doi:10.1002/1099-0690(200011)2000:223.0.co;2-1Wang, S. C., Troast, D. M., Conda-Sheridan, M., Zuo, G., LaGarde, D., Louie, J., & Tantillo, D. J. (2009). Mechanism of the Ni(0)-Catalyzed Vinylcyclopropane−Cyclopentene Rearrangement. The Journal of Organic Chemistry, 74(20), 7822-7833. doi:10.1021/jo901525uKashima, C., Fukusaka, K., & Takahashi, K. (1997). Synthesis of optically active β-lactams by the reaction of 2-acyl-3-phenyl-l-menthopyrazoles with CN compounds. Journal of Heterocyclic Chemistry, 34(5), 1559-1565. doi:10.1002/jhet.5570340529Andreu, I., Delgado, J., Espinós, A., Pérez-Ruiz, R., Jiménez, M. C., & Miranda, M. A. (2008). Cycloreversion of Azetidines via Oxidative Electron Transfer. Steady-State and Time-Resolved Studies. Organic Letters, 10(22), 5207-5210. doi:10.1021/ol802181uBelger, C., Neisius, N. M., & Plietker, B. (2010). A Selective Ru-Catalyzed Semireduction of Alkynes to Z Olefins under Transfer-Hydrogenation Conditions. Chemistry - A European Journal, 16(40), 12214-12220. doi:10.1002/chem.201001143Eicher, T., Böhm, S., Ehrhardt, H., Harth, R., & Lerch, D. (1981). Zur Reaktion von Diphenylcyclopropenon, seinen funktionellen Derivaten und Imoniumsalzen mit Aminen. Liebigs Annalen der Chemie, 1981(5), 765-788. doi:10.1002/jlac.198119810503Mazzocchi, P. H., & Thomas, J. J. (1972). Photolysis of N-methyl-2-pyrrolidone. Journal of the American Chemical Society, 94(23), 8281-8282. doi:10.1021/ja00778a085Platz, M. S., & Burns, J. R. (1979). Heteroatomic biradicals. Electron spin resonance spectroscopy of a nitrogen analog of 1,8-naphthoquinodimethane. Journal of the American Chemical Society, 101(15), 4425-4426. doi:10.1021/ja00509a086Leo, E. A., Domingo, L. R., Miranda, M. A., & Tormos, R. (2006). Photogeneration and Reactivity of 1,n-Diphenyl-1,n-azabiradicals. The Journal of Organic Chemistry, 71(12), 4439-4444. doi:10.1021/jo0601967Miranda, M. A., Font-Sanchis, E., Pérez-Prieto, J., & Scaiano, J. C. (1999). Two-Photon Generation of the 1,4-Diphenyl-1,4-butanediyl Biradical:  Direct Detection and Product Studies. The Journal of Organic Chemistry, 64(21), 7842-7845. doi:10.1021/jo990872nR. M. Wilson , in Organic Photochemistry , ed. A. Padwa , Marcel Dekker , New York , 1985 , ch. 5, vol. 7 , pp. 339–467Adam, W., Grabowski, S., & Wilson, R. M. (1990). Localized cyclic triplet diradicals. Lifetime determination by trapping with oxygen. Accounts of Chemical Research, 23(5), 165-172. doi:10.1021/ar00173a00

Ring splitting of azetidin-2-ones via radical anions

The radical anions of azetidin-2-ones, generated by UV-irradiation in the presence of triethylamine, undergo ring-splitting via N-C4 or C3-C4 bond breaking, leading to open-chain amides. This reactivity diverges from that found for the neutral excited states, which is characterised by alpha-cleavage. The preference for beta-cleavage is supported by DFT theoretical calculations on the energy barriers associated with the involved transition states. Thus, injection of one electron into the azetidin-2-one moiety constitutes a complementary activation strategy which may be exploited to produce new chemistry.Financial support from the MICINN (Grants CTQ-2010-14882, CTQ-2009-13699 and JCI-2010-06204), Generalitat Valenciana (Prometeo 2008/90), from CSIC (JAEDOC 101-2011) and from the UPV (Grant No. 20100994 and MCI Program) is gratefully acknowledged.Pérez Ruiz, R.; Sáez Cases, JA.; Domingo, LR.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2012). Ring splitting of azetidin-2-ones via radical anions. Organic and Biomolecular Chemistry. 10(39):7928-7932. https://doi.org/10.1039/c2ob26528aS79287932103

Transition metal-like carbocatalyst

Catalytic cleavage of strong bonds including hydrogen-hydrogen, carbon-oxygen, and carbon-hydrogen bonds is a highly desired yet challenging fundamental transformation for the production of chemicals and fuels. Transition metal-containing catalysts are employed, although accompanied with poor selectivity in hydrotreatment. Here we report metal-free nitrogen-assembly carbons (NACs) with closely-placed graphitic nitrogen as active sites, achieving dihydrogen dissociation and subsequent transformation of oxygenates. NACs exhibit high selectivity towards alkylarenes for hydrogenolysis of aryl ethers as model bio-oxygenates without over-hydrogeneration of arenes. Activities originate from cooperating graphitic nitrogen dopants induced by the diamine precursors, as demonstrated in mechanistic and computational studies. We further show that the NAC catalyst is versatile for dehydrogenation of ethylbenzene and tetrahydroquinoline as well as for hydrogenation of common unsaturated functionalities, including ketone, alkene, alkyne, and nitro groups. The discovery of nitrogen assembly as active sites can open up broad opportunities for rational design of new metal-free catalysts for challenging chemical reactions.The Ames Laboratory is operated for the U.S. DOE by Iowa State University under Contract No. DE‐AC02‐07CH11358. The computational simulations were performed at the OU Supercomputing Center for Education and Research and the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility, and were supported by the U.S. Department of Energy, Basic Energy Sciences (Grant DE-SC0020300). Open Access fees paid for in whole or in part by the University of Oklahoma Libraries.Ye

Ultra-wideline 14N solid-state NMR as a method for differentiating polymorphs: glycine as a case study

Nitrogen-14 solid-state NMR (SSNMR) is utilized to differentiate three polymorphic forms and a hydrochloride (HCl) salt of the amino acid glycine. Frequency-swept Wideband, Uniform Rate, Smooth Truncated (WURST) pulses were used in conjunction with Carr-Purcell Meiboom-Gill refocusing, in the form of the WURST-CPMG pulse sequence, for all spectral acquisitions. The 14N quadrupolar interaction is shown to be very sensitive to variations in the local electric field gradients (EFGs) about the 14N nucleus; hence, differentiation of the samples is accomplished through determination of the quadrupolar parameters CQ and ηQ, which are obtained from analytical simulations of the 14N SSNMR powder patterns of stationary samples (i.e., static NMR spectra). Additionally, differentiation of the polymorphs is also possible via the measurement of 14N effective transverse relaxation time constants, Teff2(14N). Plane-wave density functional theory (DFT) calculations, which exploit the periodicity of crystal lattices, are utilized to confirm the experimentally determined quadrupolar parameters as well as to determine the orientation of the 14N EFG tensors in the molecular frames. Several signal-enhancement techniques are also discussed to help improve the sensitivity of the 14N SSNMR acquisition method, including the use of selective deuteration, the application of the BRoadband Adiabatic INversion Cross-Polarization (BRAIN-CP) technique, and the use of variable-temperature (VT) experiments. Finally, we examine several cases where 14N VT experiments employing Carr-Purcell-Meiboom-Gill (CPMG) refocusing are used to approximate the rotational energy barriers for RNH3+ groups