Gold‐Catalyzed Allyl–Allyl Coupling

Abstract

Gold rings: Cationic gold(I) complexes efficiently catalyze the intramolecular allyl–allyl coupling of allyl acetates with allylstannanes with excellent stereoselectivity (see scheme). This reaction is mechanistically very different from that catalyzed by palladium.

Transmetalation between Au(I) and Sn(IV) complexes. The reaction mechanism in non-coordinating and coordinating polar solvents

“…The synthesis of the alkynyl complexes 2A-2H was easily performed in good yield (75-95%) by adding a slight excess of phenyl-alkynyl-stannane (PhC"CSn(nBu) 3 ) to a dichloromethane solution of 1A-1H complexes, according to the reaction reported in Scheme 2.…”

“…3 ] was added (0.152 ml, 0.41 mmol). After 2 h the reaction mixture was treated with activated charcoal and filtered through a Celite filter.…”

“…13 C{ 1 H} NMR (CDCl 3 , T = 298 K, ppm) : d 18.6 (oaryl CH 3 ),103.9 (AuCCPh),124.5 (AuCCPh),126.9, AuN: C,47,57;H,3,29;N,3,26. Found: C,47,44;H,3,18;N,3,20%. The following complexes were prepared under similar conditions by using the appropriate [(NHC)AuCl] precursor.…”

“…However, studies on catalytic reactions in which the key step is traceable back to the transmetalation process involving gold and tin are quite rare. In this respect, the gold catalyzed diyne cyclization involving transfer between diynes and stannyl compounds [2], the allyl-allyl coupling [3], and the alkene carbostannylation [4] represent some remarkable instances. Although the alkynyl derivatives of Au(I) can be prepared in some different methods [5], stoichiometric studies on the transfer reaction of the organic group between organotin reagents and gold(I) derivatives are rare [6] and to the best of our knowledge, no mechanistic investigations on such a reaction are reported in the literature.…”

“…Owing to the stability to air and moisture and the generally mild reaction conditions that tin derivatives require in the above cited processes, we were prompted to undertake a comprehensive investigation on the influence of the solvent and of the spectator ligands of gold complexes when reacting with stannane derivatives. In particular, we focused our attention on the reactivity and the mechanism when gold(I) substrates of the type [LAuCl] (L = DIC, PPh 3 , and NHCs) react with PhCCSn(nBu) 3 in CHCl 3 and CH 3 CN. The studied reaction yields acetylenic derivatives of gold(I) which incidentally have been hypothesized as reaction intermediates in the Sonogashire type cross-coupling reaction involving terminal alkynes and diazonium salts [7].…”