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DSpace at MIT (80,380 recursos)
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MIT Open Access Articles

Mostrando recursos 1 - 20 de 15,246

1. Rapid and Efficient Trifluoromethylation of Aromatic and Heteroaromatic Compounds Using Potassium Trifluoroacetate Enabled by a Flow System - Chen, Mao; Buchwald, Stephen Leffler
The trifluoromethylation of aryl/heteroaryl iodides has been demonstrated using a flow system, thus enabling a rapid rate of reaction. A broad spectrum of trifluoromethylated compounds was prepared in good to excellent yields using CF[subscript 3]CO[subscript 2]K as the trifluoromethyl source. The process has the advantage of short reaction times and uses convenient [CF[subscript 3]] sources.

2. Ligand-Controlled Palladium-Catalyzed Regiodivergent Suzuki–Miyaura Cross-Coupling of Allylboronates and Aryl Halides - Yang, Yang; Buchwald, Stephen Leffler
An orthogonal set of catalyst systems has been developed for the Suzuki–Miyaura coupling of 3,3-disubstituted and 3-monosubstituted allylboronates with (hetero)aryl halides. These methods allow for the highly selective preparation of either the α- or the γ-isomeric coupling product.

3. Synthesis of Aryl Sulfonamides via Palladium-Catalyzed Chlorosulfonylation of Arylboronic Acids - Niljianskul, Nootaree; DeBergh, John Robbins; Buchwald, Stephen Leffler
A palladium-catalyzed method for the preparation of sulfonamides is described. The process exhibits significant functional group tolerance and allows for the preparation of a number of arylsulfonyl chlorides and sulfonamides under mild conditions.

4. Mild and Highly Selective Palladium-Catalyzed Monoarylation of Ammonia Enabled by the Use of Bulky Biarylphosphine Ligands and Palladacycle Precatalysts - Cheung, Chi Wai; Surry, David S.; Buchwald, Stephen Leffler
A method for the Pd-catalyzed arylation of ammonia with a wide range of aryl and heteroaryl halides, including challenging five-membered heterocyclic substrates, is described. Excellent selectivity for monoarylation of ammonia to primary arylamines was achieved under mild conditions or at rt by the use of bulky biarylphosphine ligands (L6, L7, and L4) as well as their corresponding aminobiphenyl palladacycle precatalysts (3a, 3b, and 3c). As this process requires neither the use of a glovebox nor high pressures of ammonia, it should be widely applicable.

5. Mild and General Palladium-Catalyzed Synthesis of Methyl Aryl Ethers Enabled by the Use of a Palladacycle Precatalyst - Cheung, Chi Wai; Buchwald, Stephen Leffler
A general method for the Pd-catalyzed coupling of methanol with (hetero)aryl halides is described. The reactions proceed under mild conditions with a wide range of aryl and heteroaryl halides to give methyl aryl ethers in high yield.

6. Synthesis and Application of Palladium Precatalysts that Accommodate Extremely Bulky Di-tert-butylphosphino Biaryl Ligands - Bruno, Nicholas C.; Buchwald, Stephen Leffler
A series of palladacyclic precatalysts that incorporate electron-rich di-tert-butylphosphino biaryl ligands is reported. These precatalysts are easily prepared, and their use provides a general means of employing bulky ligands in palladium-catalyzed cross-coupling reactions. The application of these palladium sources to various C–N and C–O bond-forming processes is also described.

7. Palladium-Catalyzed Synthesis of N-Aryl Carbamates - Fors, Brett P.; Vinogradova, Ekaterina; Park, Nathaniel Hamilton; Buchwald, Stephen Leffler
An efficient synthesis of aryl carbamates was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of ArX (X = Cl, OTf) with sodium cyanate. The use of aryl triflates as electrophilic components in this transformation allowed for an expanded substrate scope for direct synthesis of aryl isocyanates. This methodology provides direct access to major carbamate protecting groups, S-thiocarbamates, and diisocyanate precursors to polyurethane materials.

8. Design and preparation of new palladium precatalysts for C–C and C–N cross-coupling reactions - Bruno, Nicholas C.; Tudge, Matthew T.; Buchwald, Stephen Leffler
A series of easily prepared, phosphine-ligated palladium precatalysts based on the 2-aminobiphenyl scaffold have been prepared. The role of the precatalyst-associated labile halide (or pseudohalide) in the formation and stability of the palladacycle has been examined. It was found that replacing the chloride in the previous version of the precatalyst with a mesylate leads to a new class of precatalysts with improved solution stability and that are readily prepared from a wider range of phosphine ligands. The differences between the previous version of precatalyst and that reported here are explored. In addition, the reactivity of the latter is examined in...

9. Extremely Electron-Rich, Boron-Functionalized, Icosahedral Carborane-Based Phosphinoboranes - Spokoyny, Alexander M.; Lewis, Calvin D.; Teverovskiy, Georgiy; Buchwald, Stephen Leffler
We have prepared the first examples of B9-connected trivalent aryl and alkyl phosphinoborane species via Pd-catalyzed phosphination of 9-iodo-meta-carborane. Our studies highlight the unique electronic features of the B9-connected meta-carboranyl moiety as compared to its C1-based analogue. This work suggests that the B9-functionalized meta-carboranyl substituent in these ligands exhibits more electron-releasing character than any other known carbon-based substituent, ultimately laying the foundation for a new class of phosphine ligands with extremely electron-rich character.

10. Investigating the Dearomative Rearrangement of Biaryl Phosphine-Ligated Pd(II) Complexes - Maimone, Thomas J.; Su, Mingjuan; Chen, Jiahao; Milner, Phillip John; Mueller, Peter; Buchwald, Stephen Leffler
A series of monoligated L·Pd[superscript II](Ar)X complexes (L = dialkyl biaryl phosphine) have been prepared and studied in an effort to better understand an unusual dearomative rearrangement previously documented in these systems. Experimental and theoretical evidence suggest a concerted process involving the unprecedented Pd[superscript II]-mediated insertion of an aryl group into an unactivated arene.

11. Mild and General Conditions for Negishi Cross-Coupling Enabled by the Use of Palladacycle Precatalysts - Yang, Yang; Oldenhuis, Nathan J.; Buchwald, Stephen Leffler
A wide range of biaryls were synthesized by palladium-catalyzed Negishi cross-couplings at ambient temperature or with low catalyst loading. This protocol features the use of a recently reported aminobiphenyl palladacycle precatalyst to generate the catalytically active XPhosPd[superscript 0] species. Significantly, a wide range of challenging heterocyclic and polyfluorinated aromatic substrates can be employed to give products in excellent yields.

12. Differential requirement for NMDAR activity in SAP97 -mediated regulation of the number and strength of glutamatergic AMPAR-containing synapses - Liu, Mingna; Lewis, Laura D.; Shi, Rebecca D.; Brown, Emery N.; Xu, Weifeng
PSD-95-like, disc-large (DLG) family membrane-associated guanylate kinase proteins (PSD/DLG-MAGUKs) are essential for regulating synaptic AMPA receptor (AMPAR) function and activity-dependent trafficking of AMPARs. Using a molecular replacement strategy to replace endogenous PSD-95 with SAP97β, we show that the prototypic β-isoform of the PSD-MAGUKs, SAP97β, has distinct NMDA receptor (NMDAR)-dependent roles in regulating basic properties of AMPAR-containing synapses. SAP97β enhances the number of AMPAR-containing synapses in an NMDAR-dependent manner, whereas its effect on the size of unitary synaptic response is not fully dependent on NMDAR activity. These effects contrast with those of PSD-95α, which increases both the number of AMPAR-containing synapses...

13. The effect of different spectro-temporal representations of an input auditory stimulus on the fitting of a point process model of auditory neurons - Plourde, Eric; Brown, Emery N.
We compare the effect of the use of three different spectro-temporal representations of an input auditory stimulus on the fitting of a point process model of auditory neuron firing. The three spectro-temporal representations considered are the spectrogram, a gammatone filterbank and the Hilbert spectrum. We firstly investigate how the model fits the recorded neuronal data when using either one of the three representations and secondly how well do the estimated parameters of the model correspond to their experimentally measured counterparts. It is observed that all three representations yield a model that fits well the recorded data. However, the characteristic frequencies...

14. Reconfigurable Processor for Energy-Efficient Computational Photography - Rithe, Rahul; Raina, Priyanka; Tenneti, Srikanth V.; Chandrakasan, Anantha P.; Ickes, Nathan J.
This paper presents an on-chip implementation of a scalable reconfigurable bilateral filtering processor for computational photography applications such as HDR imaging, low-light enhancement, and glare reduction. Careful pipelining and scheduling has minimized the local storage requirement to tens of kB. The 40-nm CMOS test chip operates from 98 MHz at 0.9 V to 25 MHz at 0.5 V. The test chip processes 13 megapixels/s while consuming 17.8 mW at 98 MHz and 0.9 V, achieving significant energy reduction compared with software implementations on recent mobile processors.

15. Reconfigurable processor for energy-scalable computational photography - Rithe, Rahul; Raina, Priyanka; Ickes, Nathan J.; Chandrakasan, Anantha P.; Tenneti, Srikanth V.
Computational photography applications, such as lightfield photography, enable capture and synthesis of images that could not be captured with a traditional camera. Non-linear filtering techniques like bilateral filtering form a significant part of computational photography. These techniques have a wide range of applications, including High-Dynamic Range (HDR) imaging, Low-Light Enhanced (LLE) imaging, tone management and video enhancement. The high computational complexity of such multimedia processing applications necessitates fast hardware implementations to enable real-time processing. This paper describes a hardware implementation of a reconfigurable multi-application processor for computational photography.

16. Experiment Turbulence Compensation of 50-Gbaud/s Orbital-Angular-Momentum QPSK Signals using Intensity-only based SPGD Algorithm - Xie, Guodong; Ren, Yongxiong; Huang, Hao; Lavery, Martin P.; Ahmed, Nisar; Yan, Yan; Bao, Changjing; Li, Long; Zhao, Zhe; Cao, Yinwen; Willner, Moshe; Padgett, Miles J.; Tur, Moshe; Dolinar, Samuel; Boyd, Robert; Willner, Alan; Shapiro, Jeffrey H.
An intensity-only based algorithm is employed to compensate the turbulence effects on 50-Gbaud/s orbital angular momentum QPSK channels. By only measuring the intensity profile, the purity of the OAM beams is improved and crosstalk among channels is decreased.

17. Simultaneous Pre-and Post-Turbulence Compensation of Multiple Orbital-Angular-Momentum 100-Gbit/s Data Channels in a Bidirectional Link Using a Single Adaptive-Optics System - Ren, Yongxiong; Huang, Hao; Xie, Guodong; Bao, Changjing; Li, Long; Ahmed, Nisar; Yan, Yan; Willner, Moshe; Lavery, Martin P. J.; Tur, Moshe; Neifeld, Mark; Dolinar, Samuel J.; Padgett, Miles J.; Boyd, Robert W.; Shapiro, Jeffrey H.; Willner, Alan E.
The simultaneous pre-and post-turbulence compensation of multiple orbital-angular-momentum (OAM) modes propagating through turbulent channel is experimentally demonstrated in a bidirectional free-space optical (FSO) link by using a single adaptive-optics system.

18. Improved Target-Detection Signal-to-Noise Ratio Via Quantum Illumination - Mouradian, Sara L.; Wong, Franco N. C.; Shapiro, Jeffrey H.
We report the first experimental demonstration of quantum illumination’s signal-to-noise ratio advantage over classical (laser-light) illumination for target detection in a lossy, noisy scenario.

19. Resonant Body Transistors in IBM's 32nm SOI CMOS technology - Marathe, Radhika A.; Wang, Wentao; Mahmood, Zohaib; Daniel, Luca; Weinstein, Dana
This work presents an unreleased CMOS-integrated MEMS resonators fabricated at the transistor level of IBM's 32SOI technology and realized without the need for any post-processing or packaging. These Resonant Body Transistors (RBTs) are driven capacitively and sensed piezoresistively using an n-channel Field Effect Transistor (nFET). Acoustic Bragg Reflectors (ABRs) are used to localize acoustic vibrations in these resonators completely buried in the CMOS stack and surrounded by low-k dielectric. Experimental results from the first generation hybrid CMOS-MEMS show RBTs operating at 11.1-11.5 GHz with footprints <; 5μm × 3μm. The response of active resonators is shown to contrast with passive...

20. Resonant body transistors in standard CMOS technology - Marathe, Radhika A.; Wang, Wentao; Mahmood, Zohaib; Daniel, Luca; Weinstein, Dana
This work presents Si-based electromechanical resonators fabricated at the transistor level of a standard SOI CMOS technology and realized without the need for any postprocessing or packaging. These so-called Resonant Body Transistors (RBTs) are driven capacitively and sensed by piezoresistively modulating the drain current of a Field Effect Transistor (FET). First generation devices operating at 11.1-11.5 GHz with footprints of 3μm×5μm are demonstrated. These unreleased bulk acoustic resonators are completely buried within the CMOS stack and acoustic energy at resonance is confined using Acoustic Bragg Reflectors (ABRs). The complimentary TCE of Si/SiO[subscript 2] in the resonator and the surrounding ABRs...

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