Takashi J. Ozaki

Aryl Ether as a Negishi Coupling Partner: An Approach for Constructing CC Bonds under Mild Conditions

An etheric Negishi coupling: The first cross-coupling reaction between aryl alkyl ethers and dianion-type zincate reagents to afford biaryl compounds through selective cleavage of the etheric C(sp(2))-O bond was developed. Dianion-type zincates showed excellent reactivity toward the aromatic ethers under mild conditions, with good functional group compatibility (see scheme).

How and Why Does Ni(0) Promote Smooth Etheric C-O Bond Cleavage and C-C Bond Formation? A Theoretical Study.

Ni-catalyzed cross-coupling between aryl alkyl ethers (ArOR) and Grignard reagents (RMgBr), known since 1979, proceeds under mild conditions in many cases. Although the reaction routes of various synthetic protocols involving transition-metal-catalyzed C-O bond activation have been elucidated, the mechanism of this etheric Kumada-Tamao-Curriu reaction remains enigmatic. This is because oxidative addition of inert etheric C-O to Ni(0) is thermodynamically and kinetically unfavorable, making it hard to explain the observed high reactivity of ether toward Ni catalysts. In this work, we used DFT calculations to identify a plausible reaction pathway by the Ni(0)-ate complex, which enables smooth C-O bond cleavage and R-group transfer with reasonable activation barriers; this mechanism also accounts for the ineffectiveness of Pd catalysts. These results throw new light on both C-O activation and cross-coupling, and should be valuable for further rational development of the methodologies.

Frontal-to-Parietal Top-Down Causal Streams along the Dorsal Attention Network Exclusively Mediate Voluntary Orienting of Attention

Previous effective connectivity analyses of functional magnetic resonance imaging (fMRI) have revealed dynamic causal streams along the dorsal attention network (DAN) during voluntary attentional control in the human brain. During resting state, however, fMRI has shown that the DAN is also intrinsically configured by functional connectivity, even in the absence of explicit task demands, and that may conflict with effective connectivity studies. To resolve this contradiction, we performed an effective connectivity analysis based on partial Granger causality (pGC) on event-related fMRI data during Posners cueing paradigm while optimizing experimental and imaging parameters for pGC analysis. Analysis by pGC can factor out exogenous or latent influences due to unmeasured variables. Typical regions along the DAN with greater activation during orienting than withholding of attention were selected as regions of interest (ROIs). pGC analysis on fMRI data from the ROIs showed that frontal-to-parietal top-down causal streams along the DAN appeared during (voluntary) orienting, but not during other, less-attentive and/or resting-like conditions. These results demonstrate that these causal streams along the DAN exclusively mediate voluntary covert orienting. These findings suggest that neural representations of attention in frontal regions are at the top of the hierarchy of the DAN for embodying voluntary attentional control.

Cross-Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage

Various aryl-, alkenyl-, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C-O bond to afford cross-coupled products, catalyzed by commercially available [Ni(cod)2 ] (cod=1,5-cyclooctadiene) catalysts with N-heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C-N bond cleavage in the presence of a [Pd(PPh3 )2 Cl2 ] catalyst. These methods enable selective sequential functionalizations of arenes having both C-N and C-O bonds in one pot.

Subsequent memory-dependent EEG θ correlates to parahippocampal blood oxygenation level-dependent response

The 4–12 Hz (&thgr; rhythm)-dependent neural dynamics play a fundamental role in the memory formation of the rat hippocampus. Although the power of human scalp electroencephalography &thgr; (EEG &thgr;) is known to be associated with a hippocampus-dependent memory encoding, it remains unclear whether the human hippocampus uses &thgr; rhythm. In this study, we aim to identify the scalp EEG &thgr;-related neural regions during memory encoding by using a simultaneous EEG–functional magnetic resonance imaging recording. We showed that the parahippocampal and the medial frontal and posterior regions were significantly correlated to subsequent memory-dependent EEG &thgr; power. This evidence suggests that the human parahippocampal region and associated structures use &thgr; rhythm during hippocampal memory encoding as in rodents.

Causality analysis defines neural streams of orienting and holding of attention

Previous studies with effective connectivity analysis have revealed neural streams of orienting of attention. However, neural streams involved in holding of attention on the fovea remain unclear. To identify them, we performed event-related functional MRI with a cueing paradigm and Granger causality analysis. Typical regions along the dorsal attention network (DAN) showed greater activation during orienting than during holding of attention. However, causality analysis indicated that neural streams appeared along the DAN in a top–down manner during orienting, whereas streams from widely distributed regions to the left prefrontal cortex appeared and these were dissociable from the DAN during holding of attention. Our results suggest that dissociable neural streams contribute to orienting and holding of attention, respectively.

Modified McFadyen–Stevens reaction for a versatile synthesis of aliphatic/aromatic aldehydes: design, optimization, and mechanistic investigations

The traditional McFadyen–Stevens reaction requires harsh alkaline reaction conditions, thus precluding application to the synthesis of aliphatic aldehydes. Our modified McFadyen–Stevens reaction enables the transformation from the N,N-acylsulfonyl hydrazine to the corresponding aldehyde upon treatment with an imidazole–TMS imidazole combination without relying on oxidative or reductive reagents. The reduced basicity and in situ protection of the resulting aldehyde widens the substrate scope to include aliphatic aldehydes, even ones bearing an α-hydrogen atom. Close examination of the side reactions for particular substrates in combination with theoretical considerations via DFT calculations led to a mechanistic understanding of the McFadyen–Stevens reaction involving an acyl diazene and a hydroxy carbene as reasonable intermediates.

Critical Current Properties of

The easy magnetization axis of Hg(Re)1223 is c-axis, which enables us to synthesize c-axis oriented Hg(Re)1223 polycrystalline materials using a static magnetic field. In the present study, fabrication of the c-axis oriented Hg(Re)1223 bulks was attempted by the slip-casting method in magnetic field. The Hg(Re)1223 powder sintered under various conditions was slip-cast in 8 T and 2nd-sintered under various conditions. The 2nd-sintered bulks showed Jc ~ 12 kA cm-2 at 20 K and ~ 2.4kA cm-2 at 77 K in low fields, which are quite high values for Hg(Re)1223 sintered bulks.

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Previous effective Granger causality analyses of functional magnetic resonance imaging (fMRI) have revealed dynamic causal flows along the dorsal attention network (DAN) during voluntary attentional control in the human brain. During resting state, however, fMRI studies have shown that the DAN is also intrinsically configured by functional connectivity, even in the absence of explicit task demands, and that may conflict with studies using Granger causality on visual attention. To resolve this contradiction, we performed a partial Granger causality (pGC) on event-related fMRI data during an attentional cueing paradigm while optimizing experimental and imaging parameters for pGC analysis. Analysis by pGC can factor out exogenous or latent influences from results of the analysis due to unmeasured variables. Typical regions along the DAN with greater activation during orienting (spatial cue) than withholding of attention (neutral cue) were selected as regions of interest (ROIs). pGC analysis on fMRI data from the ROIs showed that frontal-to-parietal top-down causal flows along the DAN appeared during (voluntary) orienting, but not during other, less-attentive and/or resting-like conditions. These results demonstrate that these causal flows along the DAN exclusively mediate voluntary covert orienting. These findings suggest that neural representations of attention in frontal regions are at the top of the hierarchy of the DAN for embodying voluntary attentional control. Research fund: MEXT Grant-in-Aid for Young Scientists (B) (22700281).