[4 + 2] Cycloaddition reactions of hexachlorotropone

The cycloaddition of hexachlorotropone to selected olefins, including 1,3-dienes, has been examined. Unlike tropone, which undergoes [6 + 4] cycloadditions with 1,3-dienes, only [4 + 2] processes were observed with hexachlorotropone. Its apparent preference for exo-addition (contrast tetrachlorocyclopentadienone) probably results from thermodynamic control of the endo : exo product ratios.     

[2+4] vs [4+2] Cycloaddition reactions of o-thioquinones with 1,3-dienes

Under kinetic control, the reaction of o-thioquinones with acyclic 1,3-dienes afforded, as main products, the spiro cycloadducts deriving from the participation of the thiones as dienophiles. Under thermodynamic control, or with cyclic dienes, the thioquinones behave as hetero dienes to give the benzoxathiin derivatives with complete regioselectivity.     

[4+2] Cycloaddition reactions of 1,2,4,5-tetrazines with allylcarboranes

The [4+2] cycloaddition reactions of 3,6-disubstituted 1,2,4,5-tetrazines with 9-allyl-1,7-,9-allyl-1,2-dicarba-closo-dodecaboranes and 1-allyl-2-isopropyl-1,2-dicarba-closo-dodecab-orane have been studied. The pyridazines containing carborane cage have been synthesized for the first time.     

[4+2] Cycloaddition reactions of 4-sulfur-substituted 2-pyridones with electron-deficient dienophiles

[4+2] Cycloaddition reactions of 4-(phenylthio)-1-tosyl-2-pyridone (6a) and 4-(phenylsulfonyl)-1-tosyl-2-pyridone (6b) with electron-deficient dienophiles 7 (N-methylmaleimide, N-phenylmaleimide, and methyl acrylate) gave new isoquinuclidine products 8-10. The N-tosyl group of 6a and 6b was also efficiently converted to N-alkyl derivatives 6c-f, which showed different stereoselectivity toward reactions with dienophiles 7. Several other dienophiles 15 (dimethyl acetylenedicarboxylate, methyl vinyl ketone, ethyl vinyl ether, and methyl methacrylate) were found not to react with 6a or 6b, but led to the formation of tosyl migration products 4-(phenylthio)-O-tosyl-pyridinol (16a) and 4-(phenylsulfonyl)-O-tosyl-2-pyridinol (16b), respectively. The reactivity, regioselectivity, and stereoselectivity of the cycloaddition reactions were also compared with semi-empirical calculations.     

[2+4]Cycloaddition of perfluoroazomethines

Conclusions Perfluoroazomethines react with cyclopentadiene at 160–180°C to form [2 + 4]-cycloadducts, viz., fluorine derivatives of 5-azabicyclo[2.2.1]hept-2-ene. These derivatives were used to obtain the products of the radical addition of chlorine, bromine, and bis(trifluoromethyl)-nitroxyl.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1437–1440, June, 1986.     

[4+2] Cycloaddition reactions of 1-alkyl-2,3,4,5-tetraphenylphosphole derivatives

Russian Chemical Bulletin - The [4+2] cycloaddition reactions of 1-alkyl-2,3,4,5-tetraphenylphosphole derivatives with N-phenylmaleimide were studied for the first time. The reactions of...     

[2 + 2] Cycloaddition reactions of unsymmetrically substituted carbodiimides

N-Alkyl-N′-arylcarbodiimides add alkyl and aryl isocyanates to the N-alkyl substituted CN double bond to yield 4-arylimino-1,3-diazetidine-2-ones 3. In the case of bulky alkyl substituents the reaction still proceeds across the sterically hindered CN double bond. N-Aryl-N′-[(4-dimethylamino)phenyl]carbodiimides form [2 + 2] cycloadducts with aryl isocyanates preferentially across the CN double bond not attached to the electron-rich aryl groups. However, steric crowding on this CN double bond directs the reaction to the adjacent double bond of the heterocumulative system. The rate of the [2 + 2] cycloaddition reaction of N'-methyl-N′-phenylcarbodiimide with 4-nitrophenylisocyanate is about 2.5 times faster in acetonitrile than in benzene.     

[2+2] Cycloaddition reactions of cationic iron vinylidene complexes

Complexes (Ph₃P)(Cp)(OC)Fe⁺CCR¹₂BF⁻₄ underwent [2+2] cycloaddition reactions witn the imines MeNCHR² to give the corresponding cationic iron (II) 2-azetinylidene adducts.     

有机催化不对称[4+2]环加成反应*

有机催化不对称合成反应是目前国内外研究最为活跃的领域之一。不对称[4+2]环加成（Diels-Alder）反应是合成光学活性环状化合物的有效手段,目前报道的催化不对称Diels-Alder反应的有机催化剂主要有手性咪唑啉酮、手性Br?nsted酸、手性伯胺、金鸡纳碱衍生物等。本文对各类有机催化剂在有机催化不对称Diels-Alder反应中的应用研究进展,以及不对称诱导反应的机理进行了评述。     

[3 + 4] Cycloaddition reactions of vinyl carbenoids with furans

The rhodium(II) acetate catalysed decomposition of diethyl 4-diazopent-2-enedioate in the presence of furans results in the formation of products derived from a [3 + 4] cycloaddition.     

[4+2] Cycloaddition on densely functionalized cyclopentadiene

The Diels-Alder (DA) and hetero-Diels-Alder (HDA) reaction of N-(2,4-dicyano-1,5-dimethyl-3-phenylcyclopenta-2,4-dienyl)-2,2,2-trifluoroacetamide 1 can be conveniently used for the synthesis of biarylic and polycyclic compounds, depending on whether you use alkynes or alkenes as dienophiles. We observe a totally regioselectivity and endo-diastereoselectivity of the cycloaddition reactions.     

Rhodium-Catalyzed Intermolecular [4+2] Cycloaddition of Unactivated Substrates

No electron-withdrawing or electron-releasing substituents are necessary for the substrates in the rhodium-catalyzed [4+2] cycloaddition reaction between a vinylallene and an ordinary alkyne under mild conditions [Eq. (1)]. The use of the strongly electron-accepting P[OCH(CF₃)₂]₃ ligand affords the optimal rhodium catalyst. cod = 1,5-cyclooctadiene.     

[4+3]环加成反应研究进展

本文对[4+ 3 ]环加成反应体系以及最近在合成中的应用进行了综述, 并对进一步研究的方向进行了讨论。     

钯催化[4+2]环加成反应的研究进展

综述了近年来钯催化[4+2]环加成反应的研究进展.重点讨论了钯催化[4+2]环加成反应的影响因素,如二烯体和亲二烯体、催化剂用量、配体、溶剂、反离子、温度及反应时间     

[4+2]cycloaddition reactions of triarylphosphaalkene

Cycloaddition reactions of mesityl(diphenyliiifithylene)phosphine ($\text{1}$) were Investigated. With several dienes, no Diels-Alder reactions were oEserved. With azides, diphenyidiazomethane and 2,4,6-trimethylbenzonitrile oxide, the corresponding cycloadducts ($\text{4}$$\text{12}$$\text{17}$$\text{12}$were obtained. In the case of phenyl azide, a competing Staudinger reaction occurred leading to $\text{3}$.     

Synthesis of Quinoline Derivatives by [4+2]Cycloaddition Reaction

Synthesis of quinoline derivatives by Lewis acid catalyzed [4+2]cycloaddition was investigated.     

Rhodium N-heterocyclic carbene-catalyzed [4 + 2] and [5 + 2] cycloaddition reactions

[reactions: see text] A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels-Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions, all the dienynes studied were converted to their corresponding cycloadducts in 91-99% yields within 10 min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at 15-20 degrees C. For the intermolecular [4 + 2] cycloadditions, high yields (71-99%) of the corresponding cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes studied were converted to their corresponding cycloadducts in 91-98% yields within 10 min. However, the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.     

Decarboxylative [4+2] Cycloaddition by Synergistic Palladium and Organocatalysis

A novel reaction based on synergistic catalysis, combining palladium‐ and organocatalysis has been developed. The palladium catalyst activates vinyl benzoxazinanones via a decarboxylation to undergo a [4+2] cycloaddition with iminium‐ion activated α,β‐unsaturated aldehydes. The reaction is demonstrated to proceed for a number of combinations of vinyl benzoxazinanones reacting with α,β‐unsaturated aldehydes, providing highly substituted vinyl tetrahydroquinolines in good to high yields, and excellent enantio‐ and diastereoselectivities (>98 % ee and >20:1 d.r.). The palladium catalyst used in the synergistic catalysis can be re‐used in a one‐pot sequential coupling reaction with an aromatic boronic acid forming the coupling product in 95 % yield, >20:1 d.r. and 99 % ee.     

Catalytic enantioselective [2 + 4] and [2 + 2] cycloaddition reactions with propiolamides

We report here the catalytic and highly enantioselective [2 + 4] and [2 + 2] cycloaddition reactions of electron-rich dienes or silyl enol ethers with electron-deficient propiolamide derivatives induced by copper(II).3-(2-naphthyl)-L-alanine amide complex.