Benzannulation gold-catalyzed

BENZANNULATION OF ENYNE WITH ALKYNE GOLD-CATALYZED BENZANNULATION REACTION... 

Gold Catalyst The gold-catalyzed formal [4-1-2] benzannulation reaction was reported by use of o-alkynylbenzaldehydes 11 and alkynes 2 in the presence of a catalytic amount of AuXs (X = Cl, Br), and the corresponding a-naphthyl ketones... 

The gold-catalyzed benzannulation of o-alkynylbenzaldehydes 11 proceeded not only with alkynes or alkenes, but also with carbonyl compounds 47 (Scheme 15.19) [32], The reaction proceeded even with conjugated enyne aldehydes 20. Paraldehyde 49 can be used as a masked acetaldehyde in this reaction. 

Asao et al. conducted a systematic smdy of gold-catalyzed intramolecular reactions by designing two types of substrates one a top-down approach, in which a carbon chain is attached to the carbonyl group, and the other a bottom-up approach, in which a carbon tether is extended from the alkynyl terminus [37]. As the former case, benzannulation of 59 proceeded smoothly with an AuBrs catalyst, and the corresponding tricyclic compounds 60 were produced. On the other hand, the reaction of 61 gave dihydrophenanthrenone derivatives 62 as the latter case (Scheme 15.25). 

The benzannulation method has been used as a key step for the total synthesis of some natural products. Sato et al. achieved total synthesis of the angucy-cline antibiotics (+ )-mbiginone B2 77 and (+ )-ochromycinone 78 through the gold-catalyzed intramolecular [4 - - 2] benzannulation of 75 for construction of 2,3-dihydrophenanthren-4(l//)-one skeleton 76 (Scheme 15.30) [42]. 

Dyker and Hildebrand reported the total synthesis of heliophenanthrone 83 by use of the platinum-catalyzed intramolecular benzannulation of 81 (Scheme 15.31). They also developed a method of constructing a steroid framework and chrysenone derivative 87 with gold-catalyzed annulation (Scheme 15.32) [43],... 

Transition-metal-catalyzed [4 -I- 2] benzannulation reaction of enyne with alkyne enynophile was reported by Toste group [6]. The reaction between enynes 4 and propargyl ethers 5 in the presence of a gold catalyst led to the formation of multisubstituted arenes 6 via a formal [4-1-2] cross-benzannulation reaction (Scheme 14.3). 

Scheme 52 Xue et al. s gold(l)-catalyzed synthesis of bis(benzannulated)-spiroacetals [111]...

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