Alkene derivatives arylation

The Meerwein reaction is a valuable method for the arylation of alkenes because of the easy availability of cheap aromatic amines and compounds containing double bonds. A disadvantage is that the yield is often low (normally 20-50%, in exceptional cases reaching 80%, see Table 10-3). The reaction can be carried out in water if the alkene derivative is sufficiently soluble otherwise an organic co-solvent is necessary. Meerwein et al. (1939) used acetone, which is still the most popular solvent used today. The mechanistic function of acetone will be discussed later in this section. 

Tab. 10.8 summarizes the application of rhodium-catalyzed allylic etherification to a variety of racemic secondary allylic carbonates, using the copper(I) alkoxide derived from 2,4-dimethyl-3-pentanol vide intro). Although the allyhc etherification is tolerant of linear alkyl substituents (entries 1-4), branched derivatives proved more challenging in terms of selectivity and turnover, the y-position being the first point at which branching does not appear to interfere with the substitution (entry 5). The allylic etherification also proved feasible for hydroxymethyl, alkene, and aryl substituents, albeit with lower selectivity (entries 6-9). This transformation is remarkably tolerant, given that the classical alkylation of a hindered metal alkoxide with a secondary alkyl halide would undoubtedly lead to elimination. Hence, regioselective rhodium-catalyzed allylic etherification with a secondary copper(l) alkoxide provides an important method for the synthesis of allylic ethers. 

Vinyl substitution occurs with conjugated dienes as well as with alkenes, employing aryl-, vinyl-, methyl-, alkoxycarbonyl- or benzyl-mercury reagents and lithium tetrachloropalladate(II), but the products are usually rr-allylpalladium complexes if the reactions are carried out under mild conditions (equation 8).24,25 The ir-allylic complexes may be decomposed thermally to substituted dienes26 or reacted with nucleophiles to form allylic derivatives of the nucleophile. Secondary amines, for example, react to give tertiary allylic amines in modest yields, along with dienes and reduced dienes (equation 9).25... 

Aromatic aldehydes and ketones react with carbanions to yield aryl-suhstituled alkene derivatives. 

Introduction of a Jt bond from an alkene or aryl moiety into a bicyclic system leads to significant flattening of the ring. Examples of these systems are 245A and the aromatic derivatives tetrahydronaphthalene (246) and l//-dihydroindene (247). The planar nature of the alkene moiety in 245A (see 245B) forces the four... 

The aryl palladium complexes that are formed via oxidative coupling of aryl halides with palladium(O) can undergo the Heck reaction.238,239 -p e Heck reaction is the coupling of aryl halides or aryl sulfonate esters with alkenes.340 The reaction proceeds with formation of a palladium species such as 401, with elimination of palladium to give arylated alkene derivatives.241 Aryl halides differ greatly in their reactivity, Arl being the most reactive, followed by aryl bromides. In general, aryl chlorides are very unreactive in the Heck... 

Besides the traditional coupling between alkenes and aryl (vinyl) halides, other functionalized aryl derivatives can also couple with alkenes in the Heck reaction, including aryl silanes,stannanes, bismuth, antimony,triflates, boric acid, phosphonic acid, carboxylic acid, and diazonium salt. ... 

Several independent protocols using a combination of transition metal-catalyzed stereoselective hydrosilylation, such as palladium-catalyzed crosscoupling sequence leading to stereodefined r-conjugated alkene derivatives, have been successfully developed in the last decade (4). Alkenylsilanes or siloxanes, prepared via platinum or rhodium complex-catalyzed intermolecular hydrosilylation of terminal alkynes have been highly stereospecifically cross-coupled with aryl and alkenyl halides to give unsymmetrical stilbenes, alkenylbenzenes, and conjugated dienes (Scheme 24) (4). 

Recently, Sodeoka et al. reported a Cul-catalyzed trifluoromethylation of N-protected allylaniline and homoallylaniline derivatives with Togni s reagent to tri-fluoromethylated heterocycles such as indolines in good to high yields. Both the C(sp )-H bonds of alkene and aryl rings were activated in the transformation [64] (Scheme 8.28). 

Organic azides, which are now easy to prepare and compatible with many functional groups, are a useful reagent for N-atom transfer reactions. The initial example of catalytic aziridination reactions of alkenes using aryl azides was reported by Cenini and co workers in 1999 [ 13]. In the presence of (TPP)Ru(CO) (TPP = tetraphenylporphyrin) complex as a catalyst, the reaction of cyclooctene withp-nitrophenylazidein benzene afforded the corresponding aziridine (Scheme 2.8). This reaction system can be also applied to aziridination of various styraie derivatives with aryl azides. 

Palladation products formed from arylmercurials, carboalkoxymercurials, and alkylmercurials, which have no /3-hydrogen, are used in situ for the reaction of alkenes[367]. Particularly, the arylation of alkenes is synthetically useful. Styrene derivatives 402 and 403 are formed by the reaction of a... 

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]. 

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