The intermolecular radical addition to the carbonyl group is difficult due to the facile fragmentation of the resulting alkoxyl radical. To date, the intermolecular radical addition to ketones, a valuable approach to construct quaternary carbon centers, remains a formidable synthetic challenge. Here, we report the first visible-lightinduced intermolecular alkyl boronic acid addition to αketoacids enabled by the Lewis acid activation. The in situ boron complex formation is confirmed by various spectroscopic measurements and mechanistic probing experiments, which facilitates various alkyl boronic acid addition to the carbonyl group and prevents the cleavage of the newly formed C−C bond. Diversely substituted lactates can be synthesized from readily available alkyl boronic acids and ketoacids at room temperature merely under visible light irradiation, without any additional reagent. This boron activation approach can be extended to alkyl dihydropyridines as radical precursors with external boron reagents for primary, secondary, and tertiary alkyl radical additions. The pharmaceutically useful anticholinergic precursors are easily scaled up in multigrams under metal-free conditions in flow reactors.T he carbonyl group is a readily available building block for the synthesis of substituted alcohols. 1 While the nucleophilic addition to the carbonyl group is favorable and widely studied, the radical addition to the carbonyl group is difficult, as the resulting alkoxyl radical undergoes βfragmentation readily to reverse the reaction, especially for the radical addition to ketones (Scheme 1a). 2 To date, the intermolecular radical addition to ketones, 3,4 which is valuable to construct quaternary carbon centers, 5 remains a formidable synthetic challenge. Lactates are important biological metabolites, which are precursors of poly-α-hydroxy acids for targeted drug delivery, 6 and include many prescription drugs such as anticholinergic Oxybutynin and Glycopyrrolate (see Scheme 3b for structures). 7 The α-ketoacid is a readily available synthetic building block to prepare lactates by nucleophilic additions with alkyllithiums or Grignard reagents. 8 However, these reactions are susceptible to air and moisture, and the strong nucleophilicity of these reagents unavoidably result in undesirable side reactions. 9 To this end, the new synthetic approaches to lactates, especially from different mechanistic manifolds, are in high demand.Ketoacids currently undergo decarboxylative acyl radical formations in radical reactions, and their engagement as the radical acceptors remains unknown (Scheme 1b). 10 Organoborons are environmentally friendly and readily available, and are stable synthetic building blocks with Lewis acidity. 11 In this communication, we report the first alkyl boronic acids radical addition to ketoacids with the Lewis acid activation from organoborons, which can be extended to alkyl dihydropyridine radical addition to ketoacids in the presence of external boron reagents (Scheme 1c).

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Abstract-Speech contains additional information than text that can be valuable for automatic speech summarization. In this paper, we evaluate how to effectively use acoustic/prosodic features for extractive meeting summarization, and how to integrate prosodic features with lexical and structural information for further improvement. To properly represent prosodic features, we propose different normalization methods based on speaker, topic, or local context information. Our experimental results show that using only the prosodic features we achieve better performance than using the non-prosodic information on both the human transcripts and recognition output. In addition, a decision-level combination of the prosodic and non-prosodic features yields further gain, outperforming the individual models.

Previous research has shown that the temperature of underlying permafrost decreases after the ground surface is covered with sand. No significant conclusions have yet been drawn that explain why this happens, because the heat transfer mechanism effects of the sand layer on the underlying permafrost remain unclear. These mechanisms were studied in the present work. We found that the upward shortwave radiation flux of the Qinghai-Tibet Plateau ground surface with a sand layer covering was higher than that of the surface without sand; thus, the atmospheric heat reflected by the sand layer is greater than that reflected by the surface without sand. Therefore, the net radiation of the surface with the sand layer is lower than that of the surface without sand, which reduces the heat available to warm the sand layer. Because sand is both a porous medium and a weak pervious conductor with poor heat conductivity, less heat is conducted through the sand layer to the underground permafrost than in soil without the sand deposition layer. This phenomenon results in a decrease in the ground temperature of the permafrost under the sand layer, which plays a key role in protecting the permafrost.

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The Qinghai–Tibet Railway is frequently damaged by windblown sand, and this hinders railway operation. To better understand the characteristics of windblown sand near the railway, wind tunnel experiments were conducted for the Tuotuo River Section, a typical stretch suffering from windblown sand damage. According to climate data, the windy period combines with an arid seasonal climate to increase the risk of blowing sand in this area. Wind tunnel simulation results showed how the airflow interacted with the railway embankment to create sand deposition as well as aeolian erosion. Sand transport rates behind the railbed fitted a Gaussian function well. The results can be used to guide the design of sand‐control structures both in the study area and in other areas that experience threats from windblown sand. Copyright © 2012 John Wiley & Sons, Ltd.

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