With alkenes

Equimolar quantities of tellurium tetrachloride and alkenes produce chloroalkyl tellurium trichlorides (Table 6, p. 302). The reaction of tellurium tetrachloride in chloroform with alkenes such as butenes, 1-decenes, cycloalkenes, and 3-phenoxypropenes usually gives mixtures of products arising from. syn- and 1,2-addition. Catalytic amounts of p-benzoquinone, a radical inhibitor, and acetonitrile as solvent promoted sjn-addition. In chloroform in the absence of a radical scavenger, the regiospecific, concerted xj -addition competes with the radical pathway.  

3-Chloro-2-butyl Tellurium TVichloride A 100 w/flask fitted with a magnetic stirrer is flushed with nitrogen, charged with 1.67 g (6.2 mmol) of freshly sublimed tellurium tetrachloride, 0.36 g (6.4 mmol) of (Z)-2-butenc, and 20 ml of ethanol-free chloroform, and immersed in an ice bath. The mixture is stirred for 3 h, filtered, and the filtrate is evaporated yield 1.35 g (67%), mixture of threo (80%) and erythro (20%) isomers. The mixture is recrystallized to yield the pure threo compound m.p. 107°. The erythro compound was not obtained in an isomerically pure state. 

Tellurium tetrachloride and 1-acetoxy-l-cyclohexene in diethyl ether at 20° produced 2-oxocyclohexyl tellurium trichloride.  

The compound decomposed on storage with deposition of tellurium Tellurium tetrachloride need not be used in substance it can be generated in the reaction mixture from tellurium dioxide and acetyl chloride or chlorotrimethylsilane. With acetyl bromid tellurium tetrabromide can be formed. When cyclohexene was present in the reaction mixture, 2-halocyclohexyl tellurium trihalides were isolated in approximately 70% yields. Acetic acid, chloroform, or dichloromethane may be used as solvents.  

When a solution of tellurium dioxide in concentrated hydrochloric or hydrobromic acid was added to a solution of allyl cinnamate in diethyl ether cooled to — 30°, only the allyl-double bond reacted. The allyl group rearranged during the addition of XjTe—X forming 1 -halomethyl-2-trihalotelluro-l-ethyl cinnamates. 

Cyclotelluroetherification reaction, such as shown in the accompanying equation, is discussed in Section 4.6.2.4.  

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Colourless liquid with alkenic properties. Many substituted derivatives are known, the preferred method of preparation being the addition of an alkyne to a cyclobutadiene. 

Alkylation of isoalkanes with alkenes is of particular significance. The industrially used alkylation of isobutane with isobutylene to iso-... 

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975). 

Typical nucleophiles known to react with coordinated alkenes are water, alcohols, carboxylic acids, ammonia, amines, enamines, and active methylene compounds 11.12]. The intramolecular version is particularly useful for syntheses of various heterocyclic compounds[l 3,14]. CO and aromatics also react with alkenes. The oxidation reactions of alkenes can be classified further based on these attacking species. Under certain conditions, especially in the presence of bases, the rr-alkene complex 4 is converted into the 7r-allylic complex 5. Various stoichiometric reactions of alkenes via 7r-allylic complex 5 are treated in Section 4. 

The Pd(II)-mediated reaction of benzene with alkenes affords styrene derivatives 259[230,231]. 

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

The transmetallation of various organometallic compounds (Hg, Tl, Sn, B, Si, etc.) with Pd(II) generates the reactive cr-aryl, alkenyl, and alkyl Pd compounds. These carbopalladation products can be used without isolation for further reactions. Pd(II) and Hg(II) salts have similar reactivity toward alkenes and aromatic compounds, but Hg(II) salts form stable mercuration products with alkenes and aromatic rings. The mercuration products are isolated and handled easily. On the other hand, the corresponding palladation products are too reactive to be isolated. The stable mercuration products can be used for various reactions based on facile transmetallation with Pd(II) salts to generate the very reactive palladation products 399 and 400 in rim[364,365]. 

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

Chlorobenzene reacts with alkenes with bimetallic catalyses of Ni and Pd. Chlorobenzene is converted in situ into iodobenzene (14) by the Ni-cataiyzed reaction of Nal at 140 "C. NiBr2, rather than the Ni(0) complex, is found to be a good catalyst. Then the Pd-catalyzed reaction of the iodobenzene with acrylate takes place) 15]. 

Benzyl chloride reacts with alkenes bearing an EWG[8], The reaction with acrylate proceeds smoothly to give 7-phenylcrotonate (76) in the presence of BujN without a ligand. No reaction takes place with Pd(Ph,P)4[77]. 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

The alkenyl moiety, rather than the aryl moiety, in the aryl(alkenyl)iodo-nium salt 152 reacts smoothly with alkenes under mild conditions[121]. 

Intramolecular reactions with alkenes. While the intermolecular reaction is limited to unhindered alkenes, the intramolecular version permits the participation of even hindered substituted alkenes, and various cyclic compounds are prepared by the intramolecular Heck reaction. Particularly the... 

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

The intramolecular insertion of a conjugated diene into 7r-allylpalladium, initially formed in 789, generates another rr-allyl complex 790, which is trapped with acetate anion to give a new allylic acetate 791. No further reaction of the allylic acetate with alkene takes place[489]. 

Reactions of Propargylic Compounds Catalyzed by Pd(Q) 5.2 Reactions with Alkenes and Terminal Alkynes... 

The alka-l,2,4-trienes (ailenylaikenes) 12 are prepared by the reaction of methyl propargyl carbonates with alkenes. Alkene insertion takes place into the Pd—C bond of the ailenyipailadium methoxide 4 as an intermediate and subsequent elimination of/3-hydrogen affords the 1,2,4-triene 12. The reaction proceeds rapidly under mild conditions in the presence of KBr. No reaction takes place in the absence of an alkali metal salt[4j. 

Again, it is noteworthy that 4-substituted 5-hydrdxythiazoles (24) react like 5-hydroxy-THISs with alkynes to give pyrroles and sometimes with alkenes to give exo-cycloadducts (Scheme 22). In the latter case other processes compete with the cycloaddition, becoming dominant when 24 is treated with azo-compounds, enamines, or heterocumulenes (31). 

This chapter is the first of two dealing with alkenes it describes their structure bonding and preparation Chapter 6 discusses their chemical reactions... 

Experimental measurements of dipole moments give size but not direction We normally deduce the overall direction by examining the directions of individual bond dipoles With alkenes the basic question concerns the alkyl groups attached to C=C Does an alkyl group donate electrons to or withdraw electrons from a double bond d This question can be approached by comparing the effect of an alkyl group methyl for exam pie with other substituents... 

The reachvity of the hydrogen halides reflects their ability to donate a proton Hydrogen iodide IS the strongest acid of the hydrogen halides and reacts with alkenes at the fastest rate... 

Among the hydrogen halides only hydrogen bromide reacts with alkenes by both electrophilic and free radical addition mechanisms Hydrogen iodide and hydrogen chlo ride always add to alkenes by electrophilic addition and follow Markovmkov s rule Hydrogen bromide normally reacts by electrophilic addition but if peroxides are pres ent or if the reaction is initiated photochemically the free radical mechanism is followed... 

In contrast to the free radical substitution observed when halogens react with alkanes halogens normally react with alkenes by electrophilic addition... 

In aqueous solution chlorine and bromine react with alkenes to form vicinal halohy drins, compounds that have a halogen and a hydroxyl group on adjacent carbons... 

Ozone IS a powerful electrophile and undergoes a remarkable reaction with alkenes m... 

N Bromosuccimmide provides a low concentration of molecular bromine which reacts with alkenes by a mechanism analogous to that of other free radical halogenations... 

The classification of hydrocarbons as aliphatic or aromatic took place m the 1860s when It was already apparent that there was something special about benzene toluene and their derivatives Their molecular formulas (benzene is CgHg toluene is C7Hj ) indicate that like alkenes and alkynes they are unsaturated and should undergo addition reac tions Under conditions m which bromine for example reacts rapidly with alkenes and alkynes however benzene proved to be inert Benzene does react with Bi2 m the pres ence of iron(III) bromide as a catalyst but even then addition isn t observed Substitu tion occurs instead ... 

An important property of aromatic hydrocarbons is that they are much more stable and less reactive than other unsaturated compounds Ben zene for example does not react with many of the reagents that react rapidly with alkenes When reaction does take place substitution rather than addition is observed The Kekule formulas for benzene seem mcon sistent with its low reactivity and with the fact that all of the C—C bonds m benzene are the same length (140 pm)... 

CharactenshcaUy the reagents that react with the aromatic nng of benzene and its derivatives are electrophiles We already have some experience with electrophihc reagents particularly with respect to how they react with alkenes Electrophihc reagents add to alkenes... 

The reaction of dihalocarbenes with alkenes is stereospecific and syn addition is observed... 

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