Gold-Catalyzed Cyclizations of 1,6-Diynes

Abstract

New gold-catalyzed cyclization reactions of 1,6-diynes (2,2-dipropargylmalonates) are reported. Symmetrically (Me, Et) and unsymmetrically disubstituted (Me, Et, Ph) 1,6-diynes provided stereoselectively the Z-cyclopentylidene derivatives in 31-60% and 49-83% yield, respectively. High regioselectivity (97:3) was obtained for the cyclization of Me/Ph-substituted 1,6-diynes. A monosubstituted terminal diyne afforded a cyclopentene derivative (2-acetyl-3-alkylcyclopent-2-ene-1,1-dicarboxylate, 43%), while the diterminal 1,6-diyne (2,2-di(prop-2-ynyl)malonate) produced a cyclohexenone derivative (3-methyl-5-oxocyclohex-3-ene-1,1-dicarboxylate, 61%). Plausible reaction mechanisms are proposed for the formation of the products.

Gold catalysed cyclisation reactions of 1,6-diynes triggered by the addition of methanol

“…10 The standard cyclisation experiments were carried out in methanol at room temperature in the presence of 5 mol % AuCl(PEt 3 ) or AuCl(IMes). The counter ion exchange was achieved by the addition of 6 mol % AgSbF 6 .…”

“…Such monohydration products were also identified in our previous studies. 10 A possible cyclisation of the alternative sterically demanding TMSealkyne substrate 3c was attempted, as the SieC bond length is in general larger than the equivalent CeC bond. 11 However, by goldephosphine catalysis, desilylation took place and the terminal alkyne 3b was formed, together with the monohydration product 9c (Table 1, entry 3).…”

“…7 Alcohols have further been used in gold catalysed alkoxycyclisations of 1,6-enynes to trap cationic intermediates. 8,9 We have previously reported a new gold catalysed cyclisation reaction of disubstituted 1,6-diynes 10 , providing stereoselectively Z-cyclopentylidene derivatives (I) (Scheme 1). Mono-and di-terminal 1,6-diynes afforded a,b-unsaturated cyclopentene (II) and cyclohexenone (III) products.…”

Recent advances in the gold-catalyzed additions to C–C multiple bonds

“…Enynes [110–116], diynes [117–120], allenynes [121–128], and dienes [129–131] are common substrates for intramolecular cycloaddition reactions.…”

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

“…Fiksdahl and co-workers investigated a similar gold-catalyzed transformation of internal 1,6-diynes 18 in methanol at room temperature (Scheme 14) [50–51]. Interestingly, a non-conjugated five-membered cyclic enone 19 was isolated as the product, instead of the conjugated cyclohexenone that was obtained from terminal 1,6-diynes.…”