In this article, we expand upon the catalytic hydrothiolation of 1,3-dienes to afford either allylic or homoallylic sulfides with high regiocontrol. Mechanistic studies support a pathway where regioselectivity is dictated by the choice of counter-ion associated with the Rh-center. Noncoordinating counter-ions, such as SbF 6 − , allow for η 4-diene coordination to Rh-complexes and result in allylic sulfides. In contrast, coordinating counter-ions, such as Cl − , favor neutral Rhcomplexes where the diene binds η 2 to afford homoallylic sulfides. We propose mechanisms that rationalize a fractional dependence on thiol for the 1,2-Markovnikov hydrothiolation while accounting for an inverse dependence on thiol in the 3,4-anti-Markovnikov pathway. Through the hydrothiolation of an essential oil (β-farnesene), we achieve the first enantioselective synthesis of (−)-agelasidine A.
We report a Rh-catalyzed hydrothiolation of 1,3-dienes, including petroleum feedstocks. Either secondary or tertiary allylic sulfides can be generated from the selective addition of a thiol to the more substituted double bond of a diene. The catalyst tolerates a wide range of functional groups, and the loading can be as low as 0.1 mol %.
We communicate a strategy for the hydrofunctionalization of 1,3-dienes via Rh-hydride catalysis. Conjugated dienes are coupled to nucleophiles to demonstrate the feasibility of novel C-C, C-O, C-S, and C-N bond forming processes. In the presence of a chiral JoSPOphos ligand, hydroamination generates chiral allylic amines with high regio- and enantioselectivity. Tuning both the pK and steric properties of an acid-additive is critical for enantiocontrol.
Dedicated to Professor Christian Bruneau on the occasion of his 60th birthdayOptically active b-hydroxy acids and their derivatives are versatile chiral building blocks for many useful molecules, including pharmaceuticals and natural products.[1] Catalytic asymmetric hydrogenation of b-ketoesters is an efficient and economically feasible method for preparing these important chiral compounds. Pioneered by Noyori and co-workers, [2] the chiral ruthenium diphosphine complexes [RuX 2 -(diphosphine)] (X = Cl or Br) and their analogues have become by far the most popular catalysts for this transformation.[3] Many of them show excellent enantioselectivity [> 99 % enantiomeric excess (ee)] and extraordinarily high activity (turnover number (TON) of up to 100 000) for the hydrogenation of b-alkyl b-ketoesters.[4] However, only a few of these complexes exhibit high enantioselectivity for the hydrogenation of b-aryl b-ketoesters. Zhang et al. reported that the ruthenium catalysts bearing the ligands xylyl-obinapo [5] (3,3'-bis(3,5-dimethylphenyl)-2,2'-bis(diphenylphosphinoxy)-1,1'-binaphthyl) and C 3 *-TunePhos [6] give up to 99 % ee for the hydrogenation of b-aryl b-ketoesters. Using ruthenium complexes of 4,4'-substituted binap ligands (binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), Lin et al. [7] obtained up to 99.8 % ee for the hydrogenation of a range of b-aryl b-ketoesters. The highest TON (10 000) was achieved by Saito and co-workers [8] in the asymmetric hydrogenation of methyl 3-oxo-3-phenylpropanoate. Note that chiral rhodium or iridium complexes, which efficiently catalyze olefin and imine hydrogenation, are seldom used for the asymmetric hydrogenation of b-ketoesters.[9] Furthermore, chiral [RuCl 2 (diphosphine)(diamine)] complexes, which catalyze the hydrogenation of simple ketones extremely efficiently, are also inert for the hydrogenation of b-ketoesters.[10] The major reason for the inertness may be that the strong base, such as KOtBu, that is required for activation of the [RuCl 2 (diphosphine)(diamine)] catalysts enolizes the b-ketoester substrates instead of activating the catalysts.Recently, we developed chiral iridium catalysts containing a chiral SpiroPAP ligand, and these catalysts show excellent enantioselectivity (up to 99.9 % ee) and an extremely high TON (as high as 4 550 000) for the hydrogenation of simple ketones.[11] These Ir/SpiroPAP catalysts are likely to have a "metal-ligand bifunctional catalysis" mechanism, similar to the [RuCl 2 (diphosphine)(diamine)] catalysts.[12] The aromatic N À H of the Ir/SpiroPAP catalysts is more acidic than the aliphatic NÀH of [RuCl 2 (diphosphine)(diamine)] catalysts (the proton resonances of the NH or NH 2 group of the catalysts are as follows:.3 and 3.5 ppm (C 6 D 6 ) [13] ), thus indicating that the Ir/SpiroPAP catalysts may be more easily activated with a relatively weak base such as the enolate salt of a b-ketoester. To confirm this possibility, we tested Ir/SpiroPAP catalysts for the hydrogenation of bketoesters and found that the catalysts were...
Whether prey retains antipredator behavior after a long period of predator relaxation is an important question in predator-prey evolution. Père David's deer have been raised in enclosures for more than 1200 years and this isolation provides an opportunity to study whether Père David's deer still respond to the cues of their ancestral predators or to novel predators. We played back the sounds of crows (familiar sound) and domestic dogs (familiar non-predators), of tigers and wolves (ancestral predators), and of lions (potential naïve predator) to Père David's deer in paddocks, and blank sounds to the control group, and videoed the behavior of the deer during the experiment. We also showed life-size photo models of dog, leopard, bear, tiger, wolf, and lion to the deer and video taped their responses after seeing these models. Père David's deer stared at and approached the hidden loudspeaker when they heard the roars of tiger or lion. The deer listened to tiger roars longer, approached to tiger roars more and spent more time staring at the tiger model. The stags were also found to forage less in the trials of tiger roars than that of other sound playbacks. Additionally, it took longer for the deer to restore their normal behavior after they heard tiger roars, which was longer than that after the trial of other sound playbacks. Moreover, the deer were only found to walk away after hearing the sounds of tiger and wolf. Therefore, the tiger was probably the main predator for Père David's deer in ancient time. Our study implies that Père David's deer still retain the memories of the acoustic and visual cues of their ancestral predators in spite of the long term isolation from natural habitat.
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