The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Heewon Lee - One of the best experts on this subject based on the ideXlab platform.
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carbamoyl anion addition to n sulfinyl imines highly diastereoselective synthesis of α amino amides
Journal of the American Chemical Society, 2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Maurice A. Marsini, Keith R. Fandrick, Nina C. Gonnella, Zhengxu S Han, Scot Campbell, Nelu Grinberg, Heewon LeeAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η(2) coordination of lithium by the carbonyl group.
Jonathan T. Reeves - One of the best experts on this subject based on the ideXlab platform.
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carbamoyl anion addition to n sulfinyl imines highly diastereoselective synthesis of α amino amides
Journal of the American Chemical Society, 2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Maurice A. Marsini, Keith R. Fandrick, Nina C. Gonnella, Zhengxu S Han, Scot Campbell, Nelu Grinberg, Heewon LeeAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η(2) coordination of lithium by the carbonyl group.
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Carbamoyl Anion Addition to N‑Sulfinyl Imines: Highly Diastereoselective Synthesis of α‑Amino Amides
2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Zhengxu S. Han, Maurice A. Marsini, Keith R. Fandrick, Nina C. GonnellaAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η2 coordination of lithium by the carbonyl group
Michele Zorzi - One of the best experts on this subject based on the ideXlab platform.
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optimal cognitive access and packet selection under a primary arq process via chain decoding
IEEE Transactions on Information Theory, 2016Co-Authors: Nicolo Michelusi, Petar Popovski, Michele ZorziAbstract:This paper introduces a novel technique that enables access by a cognitive secondary user (SU) to a spectrum occupied by an incumbent primary user (PU) that employs Type-I hybrid automatic retransmission request (ARQ). The technique allows the SU to perform selective retransmissions of SU data packets, whose transmission previously failed. The temporal redundancy introduced by the PU ARQ protocol and by the selective retransmission process of the SU can be exploited by the SU receiver to perform interference cancellation (IC) over multiple transmission slots, thus creating a “clean” channel for the decoding of the concurrent SU or PU packets. The chain decoding (CD) technique is initiated by a successful decoding operation of an SU or a PU packet and proceeds by an Iterative Application of IC as previously buffered packets become decodable and their interference can be removed, thus making it possible to recover the concurrent data packets, and so on, until no more packets are decodable. Based on this scheme, an optimal policy is designed that maximizes the SU throughput under a constraint on the average long-term PU performance. The optimality of the CD protocol is proved, which determines which packet the SU should send at any given time, based on four basic rules. Moreover, a decoupling principle is proved, which establishes the optimality of decoupling the secondary access strategy from the CD protocol. Specifically, first , the SU access policy, optimized via dynamic programming, specifies whether the SU should access the channel or remain idle, based on a compact state representation of the protocol, and second , the CD protocol embeds four basic rules that are used to select the packet transmitted by the SU. It is shown numerically that CD outperforms by up to 35% other schemes considered in the literature, which do not employ retransmissions at the SU pair and thus do not exploit the full potentiality of IC.
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cognitive access transmission policies under a primary arq process via chain decoding
arXiv: Information Theory, 2015Co-Authors: Nicolo Michelusi, Petar Popovski, Michele ZorziAbstract:This paper introduces a novel technique that enables access by a cognitive secondary user (SU) to a spectrum occupied by an incumbent primary user (PU) that employs Type-I Hybrid ARQ. The technique allows the SU to perform selective retransmissions of SU data packets that have not been successfully decoded in the previous attempts. The temporal redundancy introduced by the PU ARQ protocol and by the selective retransmission process of the SU can be exploited by the SU receiver to perform interference cancellation (IC) over multiple transmission slots, thus creating a "clean" channel for the decoding of the concurrent SU or PU packets. The chain decoding technique is initiated by a successful decoding operation of a SU or PU packet and proceeds by an Iterative Application of IC in order to decode the buffered signals that represent packets that could not be decoded before. Based on this scheme, an optimal policy is designed that maximizes the SU throughput under a constraint on the average long-term PU performance. The optimality of the chain decoding protocol is proved, which determines which packet the SU should send at a given time. Moreover, a decoupling principle is proved, which establishes the optimality of decoupling the secondary access strategy from the chain decoding protocol. Specifically, first, the SU access policy, optimized via dynamic programming, specifies whether the SU should access the channel or not, based on a compact state representation of the protocol; and second, the chain decoding protocol embeds four basic rules that are used to determine which packet should be transmitted by the SU. Chain decoding provably yields the maximum improvement that can be achieved by any scheme under our assumptions, and thus it is the ultimate scheme, which completely closes the gap between previous schemes and optimality.
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cognitive access policies under a primary arq process via chain decoding
Information Theory and Applications, 2013Co-Authors: Nicolo Michelusi, Petar Popovski, Michele ZorziAbstract:This paper introduces a novel technique for access by a cognitive Secondary User (SU) to a spectrum with an incumbent Primary User (PU), which uses Type-I Hybrid ARQ. The technique allows the SU to perform selective retransmissions of previously corrupted SU data packets. The temporal redundancy introduced by the primary ARQ protocol and by the selective SU retransmission process can be exploited by the SU receiver to perform Interference Cancellation (IC) over the entire interference pattern, thus creating a "clean" channel for the decoding of the concurrent message. The chain decoding technique, initiated by a successful decoding operation of a SU or PU message, consists in the Iterative Application of IC, as previously corrupted messages become decodable. Based on this scheme, we design an optimal policy that maximizes the SU throughput under a constraint on the average long-term PU throughput degradation. We show that the optimal policy can be found by first optimizing the SU access policy using a Markov Decision Process formulation, and then applying a chain decoding protocol defined by five basic rules. Such an approach enables a compact state representation of the protocol, and its efficient numerical optimization. Finally, we show by numerical results the throughput benefit of the proposed technique.
Nina C. Gonnella - One of the best experts on this subject based on the ideXlab platform.
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carbamoyl anion addition to n sulfinyl imines highly diastereoselective synthesis of α amino amides
Journal of the American Chemical Society, 2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Maurice A. Marsini, Keith R. Fandrick, Nina C. Gonnella, Zhengxu S Han, Scot Campbell, Nelu Grinberg, Heewon LeeAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η(2) coordination of lithium by the carbonyl group.
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Carbamoyl Anion Addition to N‑Sulfinyl Imines: Highly Diastereoselective Synthesis of α‑Amino Amides
2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Zhengxu S. Han, Maurice A. Marsini, Keith R. Fandrick, Nina C. GonnellaAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η2 coordination of lithium by the carbonyl group
Keith R. Fandrick - One of the best experts on this subject based on the ideXlab platform.
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carbamoyl anion addition to n sulfinyl imines highly diastereoselective synthesis of α amino amides
Journal of the American Chemical Society, 2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Maurice A. Marsini, Keith R. Fandrick, Nina C. Gonnella, Zhengxu S Han, Scot Campbell, Nelu Grinberg, Heewon LeeAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η(2) coordination of lithium by the carbonyl group.
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Carbamoyl Anion Addition to N‑Sulfinyl Imines: Highly Diastereoselective Synthesis of α‑Amino Amides
2013Co-Authors: Jonathan T. Reeves, Zhulin Tan, Melissa A. Herbage, Zhengxu S. Han, Maurice A. Marsini, Keith R. Fandrick, Nina C. GonnellaAbstract:Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative Application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η2 coordination of lithium by the carbonyl group
