A full account of the novel and flexible approach to hydroxylated 8-azabicyclo[3,2,1]octan-3-ones and 9-azabicyclo[3,3,1] nonan-3-ones is presented. Using keto-lactams as the starting materials, this two-step method c...A full account of the novel and flexible approach to hydroxylated 8-azabicyclo[3,2,1]octan-3-ones and 9-azabicyclo[3,3,1] nonan-3-ones is presented. Using keto-lactams as the starting materials, this two-step method consists of silyl enol ether for mation with TBDMSOTf, lactam activation with Tf20/DTBMP, and halide-promoted cyclization. Radical dechlorination of the resulting 1-halotropan-3-ones led to the corresponding hydroxylated tropan-3-ones, which can be hydrogenated to yield 3ct,613-dihydroxytropanes. Starting from optically active keto-lactams, the method has been applied to the enantioselective syntheses of （＋）-（1S,3S,5R,6S）-pervilleine C （6）, （＋）-（1S,3R,5S,6R）-valeroidine （3）, （＋）-（1S,3S,5R,6S）-dibenzoyloxytropane （8） and （＋）-（1S,3S,5R,6S）-merredissine （9）.展开更多
Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answerin...Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answering this question requires a clearer conceptual framework for understanding selection＇s role in speciation. We present a unified framework of speciation, pro- viding mechanistic descriptions of fundamentally distinct routes to speciation, and how these may interact during lineage splitting Two major categories are recognized： reproductive isolation resulting from （1） responses to selection, ＂speciation by selection,＂ or （2） non-selective processes, ＂speciation without selection.＂ Speciation by selection can occur via three mechanisms： （1） similar selection, （2） divergent selection, and （3） reinforcement selection. Understanding ecology＇s role in speciation requires uncovering how these three mechanisms contribute to reproductive isolation, and their relative importance compared to non-selective proce- sses, because all three mechanisms can occur side-by-side during speciation. To accomplish this, we highlight examination of groups of organisms inhabiting replicated environmental gradients. This scenario is common in nature, and a large literature illus- trates that both parallel and non-parallel responses to similar environments are widespread, and each can result in speciation. This recognition reveals four general pathways of speciation by similar or divergent selection--parallel and nonparallel responses to similar and divergent selection. Altogether, we present a more precise framework for speciation research, draw attention to some under-recognized features of speciation, emphasize the multidimensionality of speciation, reveal limitations of some previous tests and descriptions of speciation mechanisms, and point to a number of directions for future investigation [Current Zoology 59 （1）： 31-52, 2013].展开更多
The cinchona alkaloids catalyzed the direct asymmetric Mannich reactions of 1, 3-dicarbonyl compounds with acyl imines to produce novel β-amino ester derivatives containing a quinazoline moiety. The adducts were isol...The cinchona alkaloids catalyzed the direct asymmetric Mannich reactions of 1, 3-dicarbonyl compounds with acyl imines to produce novel β-amino ester derivatives containing a quinazoline moiety. The adducts were isolated with high enantiomeric excess （up to 99%）.展开更多
基金the National Basic Research Program of China(973 Program,2010CB833200)the National Natural Science Foundation of China(21072160,21332007)the Program for Changjiang Scholars and Innovative Research Team at the University of the MOE for financial support
文摘A full account of the novel and flexible approach to hydroxylated 8-azabicyclo[3,2,1]octan-3-ones and 9-azabicyclo[3,3,1] nonan-3-ones is presented. Using keto-lactams as the starting materials, this two-step method consists of silyl enol ether for mation with TBDMSOTf, lactam activation with Tf20/DTBMP, and halide-promoted cyclization. Radical dechlorination of the resulting 1-halotropan-3-ones led to the corresponding hydroxylated tropan-3-ones, which can be hydrogenated to yield 3ct,613-dihydroxytropanes. Starting from optically active keto-lactams, the method has been applied to the enantioselective syntheses of （＋）-（1S,3S,5R,6S）-pervilleine C （6）, （＋）-（1S,3R,5S,6R）-valeroidine （3）, （＋）-（1S,3S,5R,6S）-dibenzoyloxytropane （8） and （＋）-（1S,3S,5R,6S）-merredissine （9）.
文摘Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answering this question requires a clearer conceptual framework for understanding selection＇s role in speciation. We present a unified framework of speciation, pro- viding mechanistic descriptions of fundamentally distinct routes to speciation, and how these may interact during lineage splitting Two major categories are recognized： reproductive isolation resulting from （1） responses to selection, ＂speciation by selection,＂ or （2） non-selective processes, ＂speciation without selection.＂ Speciation by selection can occur via three mechanisms： （1） similar selection, （2） divergent selection, and （3） reinforcement selection. Understanding ecology＇s role in speciation requires uncovering how these three mechanisms contribute to reproductive isolation, and their relative importance compared to non-selective proce- sses, because all three mechanisms can occur side-by-side during speciation. To accomplish this, we highlight examination of groups of organisms inhabiting replicated environmental gradients. This scenario is common in nature, and a large literature illus- trates that both parallel and non-parallel responses to similar environments are widespread, and each can result in speciation. This recognition reveals four general pathways of speciation by similar or divergent selection--parallel and nonparallel responses to similar and divergent selection. Altogether, we present a more precise framework for speciation research, draw attention to some under-recognized features of speciation, emphasize the multidimensionality of speciation, reveal limitations of some previous tests and descriptions of speciation mechanisms, and point to a number of directions for future investigation [Current Zoology 59 （1）： 31-52, 2013].
文摘The cinchona alkaloids catalyzed the direct asymmetric Mannich reactions of 1, 3-dicarbonyl compounds with acyl imines to produce novel β-amino ester derivatives containing a quinazoline moiety. The adducts were isolated with high enantiomeric excess （up to 99%）.
