Iodine-catalyzed three-component reaction of quinazoline-2,5-diones with aldehydes and styrenes for the synthesis of allylamine derivatives

Iodine-catalyzed three component reaction of quinazoline-2,5-diones, aldehydes, and styrenes provides allylamine derivatives was described. Both paraformaldehyde and ethyl glyoxalate can be applied in this reaction with simple styrenes with high regioselectivity.     

1,1-Regioselective alkenylboration of styrenes enabled by palladium catalysis

Despite the 1,2-difunctionalization reactions of styrenes have been well developed, the 1,1-regioselective addition reaction remains challenging. We disclose herein a palladium-catalyzed, highly 1,1-regioselective alkenylboration of styrenes by using alkenyl triflates and a diboron reagent as the coupling partners. A wide scope of styrenes derivatives and alkenyl triflates participate this reaction to provide the corresponding allyl boronates with high regioisomeric ratios. The success of this reaction is ascribed to the application of 1,10-phenanthroline-derivated ligand and the addition of ammonium chloride salt. Moreover, acrylate esters can also selectively afford the 1,1-alkenylboration products under the same reaction conditions.     

Epoxidation of styrenes with the peroxidase from the cultured cells of Nicotiana tabacum

An enzyme concerned with the epoxidation of styrenes was isolated from cultured cells of Nicotiana tabacum. The enzyme had peroxidase activity as well as epoxidation activity, and its amino acid sequence showed 89% homology in their 9 amino acid overlap with horseradish peroxidase. In the enzymatic reaction, hydrogen peroxide and p-cresol were necessary and molecular oxygen was the source of the oxygen atom of the epoxide. The enzymatic reaction using a spin trap reagent and monitoring of the reaction with ESR indicated that the epoxidation reaction of styrenes proceeded by a radical mechanism with peroxidase.     

Aerobic photo-oxidative cleavage of the C-C double bonds of styrenes

Carbon tetrabromide enables us to carry out oxidative cleavage of the C-C double bonds of styrenes under aerobic photo-irradiation conditions. Oxidative cleavage of the various β-substituted styrenes produced benzoic acid in good yields. Since this reaction is found to be applicable to the α- or β-substituted styrenes, which showed very low reactivity under our previous cleavage reaction condition with FSM-16 and I₂, this reaction can be used complementarily.     

Cerium(IV) ammonium nitrate: Reagent for the versatile oxidative functionalization of styrenes using N-hydroxyphthalimide

Cerium(IV) ammonium nitrate was found to be a versatile reagent for the oxidative functionalization of styrenes using N-hydroxyphthalimide and iodine affording three different types of products with oxyphthalimide, nitrate and iodide groups. It was shown that reaction of styrenes with N-hydroxyphthalimide and cerium(IV) ammonium nitrate can be selectively directed to oxynitro-oxyphthalimides and dioxyphthalimides depending on the reaction conditions, in particular a solvent. Reaction of styrenes with iodine under the action of N-hydroxyphthalimide and cerium(IV) ammonium nitrate leads to the formation of iodo-oxyphthalimides.     

Novel efficient synthesis of β-fluoro-β-(trifluoromethyl)styrenes

CF₃CFBr₂ was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF₃CFBr₂ under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested.     

Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.     

Asymmetric synthesis of tetrahydroquinolines with quaternary stereocenters through the Povarov reaction

The asymmetric Povarov reaction with α-alkyl styrenes as dienophiles was catalyzed by an N,N'-dioxide L4-Sc(OTf)(3) complex. Enantiopure tetrahydroquinoline derivatives with a quaternary stereocenter at the C4 position were synthesized for the first time. A wide variety of α-alkyl styrenes and N-aryl aldimines were tolerated in the reaction, to give excellent diastereo- (up to 99:1 d.r.) and enantioselectivities (92 to >99% ee). In addition, the reaction could be performed on the gram scale without any loss of yield, diastereoselectivity, or enantioselectivity. An intermolecular hydrogen-shift reaction was found to be a side reaction, which offered a method to synthesize the corresponding quinoline derivatives with chiral quaternary sterocenters.     

Spontaneous reactions of electron‐accepting substituted quinodimethane with substituted styrenes: Inductive and steric effects on the formation of a zwitterionic intermediate

Spontaneous reactions of an electron‐accepting substituted quinodimethane, 1‐(2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione‐5‐ylidene)‐4‐(dicyanomethylene)‐2,5‐cyclohexadiene, with p‐substituted, α‐substituted, and β‐substituted styrenes were investigated. When p‐substituted styrenes were used as comonomers, no spontaneous reactions took place for styrenes with an electron‐accepting p substituent such as COOMe and CN groups, and both terpolymers and cycloadducts were formed for the other p‐substituted styrenes. When α‐substituted and β‐substituted styrenes were used as comonomers, no reactions occurred for α‐ and β‐substituted styrenes with a bulky phenyl group, and spontaneous reactions took place for those with a smaller methyl group. The reaction products were an alternating copolymer for α‐substituted styrene and both terpolymers and 5‐ethylidene‐2,5‐dimethyl‐1,3‐dioxane‐4,6‐dione for β‐substituted styrenes. The position of the methyl group in the styrenes significantly affected the product formation. This behavior in the spontaneous reactions was discussed on the basis of the ability of formation of the zwitterionic tetramethylene intermediate and its conformation, determined by polar and steric effects of the substituents in the substituted styrenes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5195–5206, 2005     

Visible‐Light‐Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives

We report a formal [4+2] cycloaddition reaction of styrenes under visible‐light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo‐ and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates.     

Visible-Light-Mediated [4+2] Cycloaddition of Styrenes: Synthesis of Tetralin Derivatives

We report a formal [4+2] cycloaddition reaction of styrenes under visible-light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo- and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates.     

Palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes

A palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes has been achieved. The reaction proceeds in a one-pot manner through 1) addition perfluoroalkyl iodides to styrenes to give benzylic iodides, 2) followed by a palladium-catalyzed Heck coupling of the resulting benzylic iodides with the same alkenes in high regio- and stereoselectivity. A variety of perfluoroalkylated alkenes were obtained in moderate to excellent yields.     

Indium(I) iodide promoted cleavage of dialkyl/diaryl disulfides and subsequent anti-Markovnikov addition to styrenes: a new route to linear thioethers

The reaction of thiolate anions, generated in situ by indium(I) iodide promoted cleavage of dialkyl/diaryl disulfides, with styrenes has been investigated. Thiolate anions add to a variety of styrenes in an anti-Markovnikov manner producing linear thioethers in high yields. This method provides a new route to the synthesis of thioethers.     

吖啶和钴肟配合物协同光催化苯乙烯放氢二聚反应构筑1,2-二氢-1-芳基萘（英文）

芳基二氢萘类衍生物是许多生物活性的天然产物以及药物的常见结构单元,其合成一直都受到化学家们的关注.传统的1,2-二氢-1-芳基萘骨架化合物的构筑大都需要进行底物的预官能团化,在高温条件下进行,且产物的选择性较差,因此发展一种简单温和的制备方法很有必要.最近兴起的可见光催化因具有条件温和、环境友好等特点而成为了合成化学家的研究热点.近期研究发现,在可见光作用下利用吖啶光敏剂的强氧化能力,可以实现苯乙烯的加成.但此类反应需要当量的氧化剂或氢原子转移试剂,容易导致苯乙烯的二聚环合产物的进一步氧化或还原.我们在前期发展的"放氢交叉偶联"反应的基础上,利用吖啶光催化和钴肟催化的协同作用,实现了苯乙烯的放氢二聚反应,在室温下高效构筑了1,2-二氢-1-芳基萘骨架,反应条件温和,底物脱除的电子和质子在钴肟催化剂作用下以氢气的形式释放,反应具有中等及以上的收率.本文以苯乙烯为模型底物,吖啶为光敏剂,钴肟配合物为质子还原催化剂,在乙腈溶剂中,蓝色LED灯下光照24 h可以获得56%的产率,对于其它的光敏剂如fac-Ⅰr(ppy)3等则不能催化该反应.通过催化剂种类及用量筛选表明,7 mol%的Co(dmgH_2)pyCl配合物具有最好的反应效果,可以获得72%的收率.控制实验表明,光敏剂、钴肟催化剂和光照都是必须的.通过底物拓展我们发现,烷基、卤素等不同取代基的苯乙烯类化合物均可以获得较好的收率,不同苯乙烯之间也可以发生交叉反应.随后,我们进一步通过光谱和中间体捕获实验对反应机理进行了研究.自由基捕获实验说明反应过程可能涉及自由基历程;光谱淬灭实验表明苯乙烯和Co(dmgH_2)pyCl均可淬灭吖啶的发光,但苯乙烯淬灭吖啶的程度远大于Co(dmgH_2)pyCl淬灭吖啶的程度.在反应时苯乙烯的浓度远大于催化剂的溶度,因此,我们认为激发态吖啶首先与苯乙烯发生反应;可见光照射反应体系1 min后在440–500和550–650 nm处观察到明显的Co~Ⅱ和Co~Ⅰ的吸收峰.基于以上实验结果,我们提出了可能的催化循环:吖啶受光激发到达激发态后,首先与底物苯乙烯发生单电子转移生成苯乙烯正离子自由基和吖啶阴离子自由基Acr~·-Mes,Acr~·-Mes还原Co(dmgH_2)pyCl生成Co ~Ⅱ中间体,从而回到基态完成光催化循环.苯乙烯正离子自由基与另一分子苯乙烯加成环合,进而通过芳构化生成自由基中间体,再与Co Ⅱ作用生成目标产物1,2-二氢-1-芳基萘和Co~Ⅰ,Co~Ⅰ通过结合体系中的质子进而释放出氢气回到Co~ Ⅲ从而完成钴肟催化循环.     

Site-selective iodine-magnesium exchange reaction of 1,4-diiodo-1,3-alkadienes by an organomagnesium ate complex,and its application to synthesis of polysubstituted styrenes and phenols

When 1,4-diiodo-1,3-alkadienes were treated with i-PrBu2MgLi, highly site-selective iodine-magnesium exchange reaction took place to afford, after the reaction with electrophiles, a variety of 1-iodo-1,3-alkadiene derivatives. Synthetic utility of the reaction was demonstrated by an efficient preparation of polysubstituted styrenes and phenols.     

Olefin Bifunctionalization: A Visible‐light Photoredox‐catalyzed Aryl Alkoxylation of Olefins

Olefin bifunctionalization is a facile route to obtain complex molecules from abundant and commercially available olefin feedstocks. Visible light together with a catalytic amount of tris(bipyridine)ruthenium salt catalyzes the aryl alkoxylation of styrenes with aryl diazonium salts in alcohol solvents via a photoredox process. The scope of this proposed reaction with respect to various aryl diazonium salts and styrenes has been investigated.     

The Huisgen 1,4-dipolar cycloaddition involving isoquinoline, dimethyl butynedioate and activated styrenes: a facile synthesis of tetrahydrobenzoquinolizine derivatives

A three-component reaction involving isoquinoline, dimethyl butynedioate and electrophilic styrenes is described. The reaction proceeds through a Huisgen 1,4-dipolar cycloaddition pathway.     

A novel multicomponent reaction involving isocyanide, dimethyl acetylenedicarboxylate (DMAD), and electrophilic styrenes: facile synthesis of highly substituted cyclopentadienes

Alkyl isocyanides, DMAD, and various activated styrenes furnish fully substituted cyclopentadienes in a one-pot three-component reaction. [reaction: see text]     

Metal and organo-catalysed asymmetric hydroaminomethylation of styrenes

A new protocol that enables asymmetric hydroaminomethylation of styrenes to afford chiral amines has been developed. Catalysed by an Rh-phosphine species and a chiral phosphoric acid, styrenes are converted into β-chiral amines with good enantioselectivities under syngas in the presence of an amine and Hantzsch ester. The reaction involves two key steps, hydroformylation and reductive amination, with the former catalysed by the Rh species whilst the latter by the phosphoric acid.     

Synthesis of trifluoromethyl alcohols from tert-butoxy-β-(trifluoromethyl)styrenes and trifluoromethylbenzyl ketones under the conditions of the Leuckart-Wallach reaction

A novel pathway towards trifluoromethylalcohols by an unexpected reaction of tert-butoxy-β-(trifluoromethyl)styrenes or corresponding trifluoromethylbenzyl ketones under the conditions of the Leuckart-Wallach reaction was elaborated.