A biomimetic total synthesis of allomicrophyllone: protective Diels-Alder reaction as a stratagem

A biomimetic total synthesis of bioactive tetracyclic natural product allomicrophyllone has been achieved in which a protective Diels-Alder reaction employing a disposable sacrificial 1,3-diene directs the regioselectivity of the subsequent Dials-Alder reaction. (C) 2010 Elsevier Ltd. All rights reserved.

Reactivity of some tetra substituted furans and thiophenes towards BF3-Et(2)O catalysed Diels-Alder reaction

Some tetra substituted furans and thiophenes were reacted with methyl acrylate under BF3-etherate catalysed Diels-Alder conditions. While the derivatives of furan underwent Diels-Alder reaction in a facile manner, an observation of 2,5-dimethyl-3,4-dianisylthiophene undergoing Diels-Alder reaction with methyl acrylate is remarkable. (C) 1997, Elsevier Science Ltd.

Unprecedented formation of a 14-membered dihydropyran macrocycle via sequential olefin cross metathesis-intramolecular hetero Diels-Alder reaction

Formation of a 2,3-dihydro-4H-pyran containing 14-membered macrocycle by sequential olefin cross metathesis and a highly regiospecific hetero Diels-Alder reaction was observed in the reaction of a hydroxydienone derived from tartaric acid with Grubbs' second generation catalyst. It was found that the free alcohol in the hydroxyenone led to the macrocycle formation, while protection of the hydroxy group formed the ring closing metathesis product. (C) 2013 Elsevier Ltd. All rights reserved.

Advances in organic catalysis: the design of a novel asymmetric, organocatalytic intramolecular Diels Alder reaction

No abstract.

无水稀土氯化物催化下Diels-Alder反应的研究

本文研究了在无水氯化稀土催化下2－甲基呋喃和丙烯醛、呋喃和丙烯醛、呋喃和丙烯酸甲酯、2－甲基呋喃和丙烯酸甲酯，呋喃和丙烯酸乙酯以及丁二烯和顺丁烯二酸酐的Diels-Aldel反应，结果表明:（1）无水LnCl_3 (Cn=Nd, Eu, Gd, Yb)对2－甲苯呋喃和丙烯醛的反应有明显的催化作用，反应在温和条件下（25℃，常压无溶剂）顺利进行，不同LnCl_3催化活性按稀土元素原子序数递增而增加。其中，仅用0.008mol% YbCl_3就可催化反应达到85％的产品收率。本反应是连串反应，产物在LnCl_3催化下聚合成低聚物，适当降低催化剂用量是控制产物的聚合从而提高产品收率。与AlCl_3相比，YbCl_3的活性比AlCl_3高。降低反应温度也可以相对控制副反应。当丙烯醛和2－甲基呋喃的用量摩尔比为2:1时，反应能得到最好结果。用THF作溶剂时反应产率比甲苯作溶时要低得多。（2）丙烯醛和呋喃在常温下经CnCl_3催化可得到反应物摩尔比为1：1和2：1两种加成物，主要是2：1加成物。1：1加成物在LnCl_3存在下易聚合，在加热下易聚合。室温下易分角为原料。本反应在－40℃以CH_2Cl_2为溶剂YbCl_3催人时，只得到1：1加成物但收率不高.（3）LnCL_3对呋喃和丙烯酸甲酯的反应有良好的催化活性，当温度为40℃，YbCl_3 10mol%, 反应60小时可得到N/X = 17/27的产物2-carbomethoxy-7-oxabicyclo [2. 2. 1]nept-5-ene, 收率为80％。温度的降低有利地内型产物的生成，反应时间，催化剂用量对反应产物收率和立体选择性都有影响。（4）2－甲基呋喃和丙烯酸甲酯在YbCl_3催化下比（3）的反应更易进行。0℃时，6mol% YbCl_3反应67小时，收率可达88％，产物N/x达3.0。温度的降低有利于内型产物的生成，而反应时间和催化剂用量不影响产物立体选择性。（5）呋喃和丙烯酸乙酯 在10mol% YbCl_3催化下室温反应48小时，得到N／X＝Y_(1.47)的产物44％。温度的降低有利于内型产物的生成，反应时间相对处长有利于产品收率但不影响产品的立体选择性。此外，我们分离得到丙烯酸乙酯和YbCl_3的络合物，证明反应首先是通过YbCl_3和羟基氧的络合，然后再和双烯加成。（6）不同LnCl_3对丁二烯和顺丁烯二酸酐的反应具有不同催化活性，其活性按稀土元素原子序数递增而增加，即：LaCb < PrCl_3 , SmCl_3 < EuCl_3 < GdCl_3 < YbCl_3.

Glass wafers bonding via Diels-Alder reaction at mild temperature

In this paper, we introduced a novel bonding method of glass wafers by Diels-Alder reaction at mild temperature. After standard hydroxylization and aminosilylation, two wafers were modified by 2-furaldehyde and maleic anhydride, respectively. Then they were brought into close contact and tightly held with a clamping fixture. A strong bonding could be achieved by annealing for 5 h at 200 degrees C. Bonding strength is as high as 1.78 MPa and sufficient for most application of microfluidic chips.

电子反常供需型Diels-Alder反应合成2-吡啶基吡啶

电子反常供需型Diels-Alder反应(inverse electron demabd Diels-Alder reaction,IDA)因其在天然生物碱及类似物合成中的应用,在近20年来已经逐渐引起关注[1].含氮芳杂环体系1,2,4-三嗪由于其特有的缺电子特征,作为双烯体非常适于进行这类反应[2].本文利用IDA反应从3-吡啶基-5,6-二取代-1,2,4-三嗪出发,设计出一条简捷、低成本的合成路线,成功地合成出不对称取代的2,3′-联吡啶和2,4′-联吡啶.这一类化合物已被应用于药物中间体或有机配体.

无水稀土氯化物催化丁二烯和顺丁烯二酸酐的Diels-Alder反应

稀土化合物在有机合成中特别是在Diels-Alder反应中的应用是近年来稀土化学中最引人注目的研究课题之一。对于某些难进行的Diels-Alder反应,使用Lewis酸作催化剂可缓和反应条件,提高产物收率,改善产物选择性。其中,含稀土离子的Lewis酸在某些反应中显示了比其它Lewis酸更高的催化活性和产物具有更高的选择性。本文报道以丁二烯和顺丁烯二酸酐为原料,用7种简便易得的稀土氯化物催化这一Dies-Alder反应的结果。

DIELS-ALDER REACTION CATALYZED BY RARE-EARTH CHLORIDES

Rare earth chlorides were used to catalyze the synthesis of 2-butoxy-3, 4-dihydro-2H-pyran using equimolar acrolein and vinyl butyl either. The cycloadduct is unstable which undergoes catalytic ring opening oligomerization. The way to stabilize the cyclo adduct has been studied, thus high yields of 90-95% were obtained.

Ergosterimide, a new natural Diels-Alder adduct of a steroid and maleimide in the fungus Aspergillus niger

Ergosterimide (1), a natural Diels-Alder adduct of ergosteroid and maleimide, was characterized from the culture extract of Aspergillus niger EN-13, an endophytic fungus isolated from the marine brown alga Colpomenia sinuosa. In addition, four known steroids including (22E,24R)-ergosta-5,7,22-trien-3 beta-ol (2), (22E,24R)-ergosta-4,6,8(14),22-tetraen-3one (3), (22E,24R)-5 alpha,8 alpha-epidioxyergosta-6,22-dien-3 beta-ol (4), and (22E,24R)-ergosta-7,22dien-3 beta,5 alpha,6 beta-triol. (5) were also isolated and identified. The structures of these compounds were elucidated by extensive analysis of 1D and 2D NMR and IR spectra and MS data. The plausible biosynthetic pathway of 1 was also discussed. To the best of our knowledge, 1 is the first natural Diels-Alder adduct of steroid and maleimide reported so far. (C) 2007 Elsevier Inc. All rights reserved.

Ionic Liquid Effect on the Reversal of Configuration for the Magnesium(II) and Copper(II) Bis(oxazoline)-Catalysed Enantioselective Diels-Alder Reaction

Ionic liquids have been used to support a range of magnesium-and copper-based bis(oxazoline) complexes for the enantioselective Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene. Compared with reaction performed in dichloromethane or diethyl ether, an enhancement in ee is observed with a large increase in reaction rate. In addition, for non-sterically hindered bis(oxazoline) ligands, that is, phenyl functionalised ligands, a reversal in configuration is found in the ionic liquid, 1-ethyl-3-methylimidazolium bis[(trifluoromethanesulfonyl)imide], compared with molecular solvents. Supported ionic liquid phase catalysts have also been developed using surface-modified silica which show good reactivity and enantioselectivity for the case of the magnesium-based bis(oxazoline) complexes. Poor ees and conversion were observed for the analogous copper-based systems. Some drop in ee was found on supporting the catalyst due a drop in the rate of reaction and, therefore, an increase in the contribution from the uncatalysed a chiral reaction.

Synthesis of , of α,β-unsaturated aldehydes and nitriles via cross-metathesis reactions using Grubbs’ catalysts

A series of alpha,beta-unsaturated aldehydes and nitriles of significant interest in the fragrance industry have been prepared using Grubbs' catalysts in cross-metathesis reactions of electron-deficient olefins (i.e., acrolein, crotonaldehyde, methacrolein, and acrylonitrile) with various 1-alkenes, including 1-decene, 1-octene, 1-hexene and 2-allyloxy-6-methylheptane. The latter is of particular interest, as it has not previously being used as a substrate in cross-metathesis reactions and allows access to valuable intermediates for the synthesis of new fragrances. Most reactions gave good selectivity of the desired CM product (>= 90%). Detailed optimisation and mechanistic studies have been performed on the cross-metathesis of acrolein with 1-decene. Recycling of the catalyst has been attempted using ionic liquids. 

Convergence of products from Povarov and von Miller reactions: approaches to helquinoline

Yttrium triflate or triflic acid catalysed Povarov reaction of methyl anthranilate with ethyl vinyl ether, both as aldehyde surrogate and as alkene, gave the desired 2-methyl-4-ethoxytetrahydroquinoline diastereoisomers as the major products along with four component coupling von Miller adducts. A proton NMR-study, using yttrium triflate as catalyst, revealed that the cis-diastereoisomers were the initial major products in both the Povarov and von Miller reactions but that these isomerised to the trans-diastereoisomers under the reaction conditions. Two distinct pathways for forming von Miller adducts were uncovered with the initial Povarov products being converted to von Miller adducts under the reaction conditions. Replacement of the 4-ethoxy with a 4-methoxy group under acidic conditions gave predominantly the trans-diastereoisomer, which was subsequently converted to a cis/trans mixture of the tetrahydroquinoline antibiotic helquinoline. It was also possible to convert the von Miller products to Povarov products under acidic conditions