Allenes hydroarylation

A highly electrophilic phosphite gold(I) catalyst was applied to the intramolecular allene hydroarylation reaction to give a vinyl-substituted carbocycle [17], This cyclization proceeds effectively in cases where the aryl groups are electron-rich arene nucleophiles. A dimethoxybenzene bearing an allene group furnished a vinyl-substituted tetralin derivative in 85% yield (Scheme 18.18). From the mechanistic... 

Study on this allene hydroarylation reaction, the presence of dinuclear gold-gold and gold-silver intermediates was suggested (Scheme 18.19), together with vinyl gold complex, in the gold(I)-catalyzed hydroarylation [18],... 

Although less studied than O- and N-nueleophiles, other nueleophilic partners possessing H-X bonds can participate in gold-eatalyzed hydrofunctionalization reactions. Hence, the intermoleeular hydroarylation ie. C(sp2)-H bond addition] of allenes with indoles was reported in the presence of [(IPr) AuCl]. Using the same catalyst, Che and co-workers investigated an interesting cascade terminated by an alkyne hydroarylation step. The intramolecular allene hydroarylation with indoles was also described by Alcaide and Almendros. ... 

Very recently, Fujii and Ohno developed a route for the synthesis of dihydroquinoline and chromene derivatives under mild reaction conditions. Hydroarylation leads to a highly selective formation of six-membered rings, depending on the carbon (terminal or central allenic) that reacts with the aryl moiety [50]. 

In the context of the total synthesis of ( )-rhazinilam, an intramolecular hydroarylation of an allene (Scheme 12.23) was investigated.41 The authors report that the Ag(I) complexes were completely ineffective, while AUCI3 delivered 27% of the product and a mixture of 5 mol% AuC13/20 mol% AgOTf gave 82%. The optimum was then reached with 5 mol% Ph3PAuOTf (92% yield). In all cases, the diastereoselectivity was better than 92 8. 

The first carbon addition to allenes catalyzed by gold was described by Hashmi and was the addition of furans to allenones, a reaction that is discussed as a conjugate addition to carbonyls. Then the annulation of 2-allenyl indoles was described (equation 111)and an enantioselective version was later developed for terminal allenes. Then Nelson described the cyclization of an N-substituted pyrrol in the synthesis of (—)-Rhazinilam (equation 112). In that case, gold notably improved the yields and selectivities obtained with Pd(II) or Ag(l), and gave complete retention of the chiral information of the allene. The most recent report is on the hydroarylations of allenes with gold-covered substituted benzenes as substrates. ""... 

Representative procedure for the intramolecular gold-catalyzed hydroarylation of allenes. (R,E)-Methyl 4-[(R)-8-ethyl-5,6,7,8-tetrahydroindolizin-8-yl]-2-methylbut-3-... 

Electron-rich phenyl rings are also suitable nucleophiles for the intramolecular gold-catalyzed hydroarylation of allenes. Thus, dihydroquinoline and chromene derivatives are accessible by treating allenic anilines or allenic aiylethers with a cationic gold catalyst (Scheme 4-14). Because of the limited stability of... 

Intermolecular hydroarylations of terminal allenes with highly nucleophilic methoxyarenes are catalyzed by cationic phosphite gold(l) complexes. The addition takes place regioselectively at the unsubstituted allene terminus and affords ( )-allylated benzene derivatives with moderate-to-high yields. 

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. ... 

Indenes can be synthesized via intramolecular hydroarylation of propargyl acetates catalyzed by NHC gold(I) complexes [127, 128]. The formation of the indenes proceeds via a 1,3-shift to form an allene, followed by the hydroarylation (Scheme 1.8). Notably, this reaction requires strictly anhydrous conditions, because conjugated enones and enals are isolated in the presence of water [129]. Related transformations include reaction with propagyl sulphides or dithioacetals. 

Even though less studied than the O- and A-nucleophiles, other important H-X bonds can participate in hydrofunctionalization catalyzed by gold. Hence, the intermolecular hydroarylation i.e. bond addition) of allenes... 

Alkenes undergo intramolecular hydroarylation under conditions similar to those for allenes. Aromatic compounds bearing alkene side chains afford tetralin derivatives. The intramolecular hydroarylation reaction is catalyzed by RuCls/AgOTf (Scheme 18.10) [9] or Bi(OTf)3 (Scheme 18.11) [10]. The latter process was applied to a tricyclic compound and a seven-membered ring product. The intramolecular hydroarylation of 5-phenylpent-l-ene in the presence of AuCb/AgOTf catalyst affords 1-methyltetralin in 98% yield (Scheme 18.12) [11]. 

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