Hydroarylation catalysed

Hydroarylation, (addition of H-Ar, Ar = aryl), of alkynes, catalysed by Pd(OOCCH3)2 or Pd(OOCCFj)j in acetic acid, is an atom-economic reaction, giving rise to substituted c/i-stilbenes (Fujiwara reaction). Catalytic conversions and improved chemoselectivity to the mono-coupled product under mild conditions can be achieved by modification of the metal coordination sphere with NHC ligands. Hydroarylation of mesitylene by ethylpropiolate (Scheme 2.19) catalysed by complex 107 (Fig. 2.18) proceeds in good conversions (80-99%, 1 mol%) under mild conditions at room temperature. 

The intramolecular hydroarylation/cyclisation of aryl propargylic acetates catalysed by the system [AuCl(IPr)]/AgBF (1 1, 2 mol%, 72-92%, rt, 5 min) was developed as a versatile and efficient method leading to indene derivatives 110 (Scheme 2.20). Analogous catalytic systems, where the IPr was substituted by PPh, gave lower conversions and chemo-Zregio-selectivity. 

Scheme 6.15 Pd-catalysed hydroarylation or norbornene using chelating NHC/P-Ugands...

The allylic alcohols 41 derived from the propynols 40 by either a regioselective Pd-catalysed hydroarylation or hydrovinylation are readily cyclised to 4-aryl or 4-vinyl 2//-chromenes in high yield (Scheme 27) <00EJO4099>. 

Coumarins are formed by the intramolecular hydroarylation of an activated alkyne. The basic starting materials for this fast, efficient and general Pd-catalysed reaction are phenols and alkynoic acids (Scheme 42), An intermolecular version in which electron-rich phenols react with 4-methoxycinnamic acid leads to high yields of 3,4-dihydrocoumarins... 

A highly regio- and stereo-selective Brpnsted acid-catalysed addition of aromatic heterocycles, such as pyrroles, furans, and indoles, to ynamides RC=CN(R)(EWG), catalysed by Tf2NH at —35 °C, has been developed as an equivalent of hydroarylation of ynamides.41... 

Asymmetric hydroarylation of diphenylphosphinylallenes [Ph2P(0)]C(R)=C=CH2 with arylboronic acids ArB(OH)2, catalysed by an Rh-BINAP complex, has been shown to proceed in high yields with high regio- and enantio-selectivity to afford chiral allylphosphine oxides [Ph2P(0)]CH(R)C(Ar)=CH2 of up to 98% ee. A Tr-allylrhodium complex has been identified as the key intermediate.109... 

The cationic binuclear complex [(Mes3PAu)2Cl]BF4 has been found to catalyse the reaction of 2-methyl- or 2-pentyl-furan (78) with phenylacetylene, pent-l-yne, or hept-l-yne (79) to afford the products of a twofold hydroarylation of the alkyne (80).120... 

PtC /AgOTf-catalysed hydroarylation of ethyl propiolate, HC CCC Et, with ArH in CF3CO2H has been developed as a method for the preparation of ethyl (Z)-cinnamates, (Z)-ArCH=CHC02Et, in good to high yields, without the formation of... 

The catalytic functionalization of aromatic C-H bonds to form C-C bonds under mild conditions is an attractive economic objective. An efficient hydroarylation reaction between alkynes and alkenes to form C-C bonds has been described.43 The reactions are catalysed by Aum complexes under mild and even solvent-free conditions at ambient temperature. 

Aryl and 4-vinyl derivatives of 2,2-dialkylchromenes have been obtained from the Pd-catalysed reaction of tertiary 3-(2-bromophenyl)propynols 9 with aryl iodides and vinyl triflates, respectively. The sequential hydroarylation/hydrovinylation and cyclisation steps can be carried out in a one-pot process <06SL909>. 

Zhong et al. used their phosphino functionalised carbene ligands successfully in the palladium catalysed hydroarylation of bicyclic alkenes. 

No racemisation is observed during the Pt(IV)-catalysed cyclisation of chiral propargyl ethers to chromenes. The PtCU catalyst appears to activate selectively the triple bond to nucleophilic attack by the arene and enables this well-established route to chromenes to be carried out under mild, neutral conditions and with a variety of substrates (Scheme 12) <03T8859>. A Pt-catalysed 6-endo hydroarylation of an alkynone combined with an intramolecular Michael addition are the key steps in a synthesis of the rotenoid deguelin <030L4053>. 

Palladium-catalysed hydroarylations and hydrovinylations of olefins and acetylenes have been reviewed. Vinyl iodide, for instance, reacts with internal acetylenes in the presence of (PPh3)2Pd(OAc)2, triethylamine and formic acid to yield the alkenes 204... 

Arylchrom-3-en-2-ols and 3-arylcoumarins are accessible from 3,3-diethoxyprop-l-yne through sequential Pd-catalysed coupling with aryl halides and hydroarylation and finally cyclisation <97SL1367>. A facile cyclisation of o-(3-hydroxy-3-methylbutynyl)phenols effected by BBr3 leads to 4-bromo-2,2-dimethylchromenes the bromine can be removed by electrolytic reduction <97H(45)1131>. 

Asymmetric hydroarylation of styrenes and dienes RCH=CH2 with arylboronates ArB(OR)2, catalysed by (5 )-(Pr Box)PdCl2 (7.5 mol%) and Bu OK (5 mol%), can be attained under oxygen atmosphere to produce RCH(Ar)-Me with <75% ee. The competing -elimination is largely suppressed under these conditions. ... 

An asymmetric version of the intramolecular hydroarylation of alkynes (286) to produce fused rings (287) has been developed. With the cationic Pd(II)/(5)-(285) catalyst, the resulting 4-aryl 2-quinolinones were obtained with <98% ee. Asymmetric addition of boronic acids R B(OH)2 to activated cumulenes R C=C=C=C(R )C02Et, catalysed by an NHC-palladium complex, has been shown to yield allenic products R C=C=C(R )CH(R )C02Et with moderate to good enantioselectivities. ... 

Desulfitative hydroarylation of alkynes R C=CR with sodium salts of sulfinic acids ArS02Na, catalysed by (AcO)2Pd at 120 °C, has been reported to produce the syn-adducts ( )-RiCH=C(Ar)R2. 5... 

Ruthenium(II) biscarboxylate complex (101) has been reported to catalyse hydroaryla-tions of unactivated alkenes RCH=CH2 with Ar-H through C-H bond activation, giving rise to ArCH2CH2R. ° The same complex is capable of promoting hydroarylations and hydroalkenylations of methylenecyclopropanes (107) with the a-pyridyl derivative (106) to produce (108). ° ... 

Rhodium complexes with the ferrocenyl ligand (i ,5)-Cy2PF-PPh2 (109) have been shown to catalyse asymmetric hydroalkynylation of norbornadienes with <99.9% ee A hydroxorhodium complex with (R)-Segphos (110) has been shown to catalyse the hydroarylation of 3-pyrrolines (111) with arylboroxines (112) under neutral conditions to give 3-arylpyrrolidines (113) (<96% ee) ... 

An In(III)-catalysed selective 6-exo-dig hydroarylation of o-propargylbiaryls and subsequent double-bond migration has been reported to give funetionalized phenanthrenes (Scheme 135).i94... 

Scheme 7.67 Tandem hydroamination-hydroarylation-transfer hydrogenation reaction catalysed by gold catalysis and chiral phosphoric acid...

Abstract The selective catalytic activation/functionalization of sp C-H bonds is expected to improve synthesis methods by better step number and atom economy. This chapter describes the recent achievements of ruthenium(II) catalysed transformations of sp C-H bonds for cross-coupled C-C bond formation. First arylation and heteroarylation with aromatic halides of a variety of (hetero)arenes, that are directed at ortho position by heterocycle or imine groups, are presented. The role of carboxylate partners is shown for Ru(II) catalysts that are able to operate profitably in water and to selectively produce diarylated or monoarylated products. The alkylation of (hetero)arenes with primary and secondary alkylhalides, and by hydroarylation of alkene C=C bonds is presented. The recent access to functional alkenes via oxidative dehydrogenative functionalization of C-H bonds with alkenes first, and then with alkynes, is shown to be catalysed by a Ru(ll) species associated with a silver salt in the presence of an oxidant such as Cu(OAc)2. Finally the catalytic oxidative annulations with alkynes to rapidly form a variety of heterocycles are described by initial activation of C-H followed by that of N-H or O-H bonds and by formation of a second C-C bond on reaction with C=0, C=N, and sp C-H bonds. Most catalytic cycles leading from C-H to C-C bond are discussed. 

Hydroarylation of alkenes offers a more atom-economical process of catalytic C-H bond alkylation. It involves the transition-metal catalysed formal addition of the arene C-H bond onto C=C bonds. Especially T. B. Gtiimoe and his group have shown that ruthenium(II) catalysts favour the addition of aromatic C-H bonds to an olefin C=C bond. They have used ruthenium(II) catalysts of type TpRu-R(L) (NCMe) (Tp=hydrotris(pyrazolyl)borate) and demonstrated the efficiency of the formation of ethylbenzene via catalytic addition of benzene to ethylene [(Eq. 37)] [113-118]. Analogously the same type of catalyst TpRu-R(L)(NCMe) promotes the alkylation by ethylene at C2 position of furan and thiophene [119]. 

Scheme 11 Proposed mechanism for the Ru(II)-catalysed hydroarylation of ethylene...

Under conditions of mthenium(ll) catalysed sp C-H bond activation of phenyl pyridine Ackermann has shown the direct intermolecular hydroarylation of highly... 

Various functional alkenes were similarly synthesized with high regio and E-stereoselective manner via [RuCl2(p-cymene)]2/AgSbF6 catalysed hydroarylation of phenyl or ester substituted alkynes with aromatic carbamates. The addition of 5 equiv. of pivalic acid improves the reaction in 1,4-dioxane. The alkenyl ester is converted into carboxylic acid by using 2 equiv. of LiOH, whereas phenol derivatives were deprotected by addition of 10 equiv. of LiOH [(Eq. 82)] [166]. 

Scheme 8.5 Cobalt-catalysed intramolecular olefin hydroarylation on indole derivatives.

A comprehensive DFT/M06 study of the hydroarylation of the 2-(haloethynyl)biphenyl derivatives, catalysed by various metal complexes, has shed new light on the subtle difference between InCl3, AuCl, and PtCl2 catalysts as alkyne activators, and demonstrated... 

The ruthenium-catalysed hydroarylation of alkynes (151) with benzamides (150) has been reported to proceed regio- and stereo-selectively and is believed to involve the amide-directed ort/to-metallation, carbometallation of the alkyne, and protonolysis. Phenylazoles exhibit similar reactivity and regioselectivity. ... 

Ruthenium-catalysed hydroarylation of highly strained methylenecyclopropanes, such as (153), with 2-phenylpyridine (154) and related substrates that offer the chelation-assisted C-H activation to produce (155), has been reported. A plausible mechanistic rationale and a catalytic cycle have been proposed, based on labelling experiments. ... 

Gold-catalysed intramolecular hydroarylation of [(3-arylprop-2-ynyl)oxy]benzene derivatives (258) has been shown to proceed readily as a (> CY-endo-dig process with a hydrogen transfer (highhghted) to afford (259). ... 

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