An enantioselectiveDiels–Alder reaction of 3-nitrocoumarins has been developed. A tryptophan-derived C 1-symmetric organoammonium thiourea catalyst promoted the reaction of 3-nitrocoumarins with Danishefsky’s diene to give the corresponding adducts with good enantioselectivity (up to 94% ee). One of the resulting adducts was converted into a chiral carbocyclic quaternary β-amino alcohol.
已经开发了 3-硝基香豆素的对映选择性 Diels-Alder 反应。色氨酸衍生的 C 1-对称有机铵硫脲催化剂促进了 3-硝基香豆素与丹麦谢夫斯基二烯的反应,得到具有良好对映选择性(高达 94% ee)的相应加合物。所得加合物之一被转化为手性碳环季 β-氨基醇。
3-Nitrocoumarins as Dienophiles in the Diels−Alder Reaction in Water. An Approach to the Synthesis of Nitrotetrahydrobenzo[<i>c</i>]chromenones and Dihydrodibenzo[<i>b</i>,<i>d</i>]furans
cyclopentadiene (12) were investigated in aqueous medium, in organic solvent and under solventless conditions. The reactions performed in water occurred in heterogeneous phase but were faster than those executed in toluene or dichloroethane (DCE). 1a-c, 5, and 6 behaved as 2pi components in the Diels-Alder cycloadditions with 7-10 and 12, and exo adducts were preferentially or exclusively produced. Surprisingly
Abstract C 1-Symmetric chiral ammonium salt catalysts induced a kinetic resolution of racemic α-nitrolactones through an asymmetric ester–amide exchangereaction. The corresponding amides were obtained with high enantioselectivities and high S (= k fast/k slow) values. This reaction system is a useful approach for obtaining carbocyclic quaternary α-nitroamides as chiral building blocks. Publication
The one-pot synthesis of multisubstituted pyrazole derivatives was achieved viacatalyst-free 1,3-dipolar cycloaddition of ethyl diazoacetate and nitroalkenes as the key step and elimination of the leaving group (NO2 or Br) followed by intramolecular proton transfer with satisfactory yields.
(ethyl vinylether (8), 2,3-dihydrofuran (9), and 3,4-dihydro-2H-pyran (10)) were investigated in water, in neat conditions, and in organic solvents. The cycloadditions do not require the use of catalysts and are highly endo diastereoselective, and in water the cyclic nitronates 13, 18, and 23 are converted into chromene derivatives via hydrolysis, decarboxylation, and acetalation reactions. A one-pot