Gold(I)-Catalyzed Divergence in the Reactivity of 3-Silyloxy 1,6-Enynes: Pinacol-Terminated vs Claisen-Terminated Cyclization Cascades

Abstract

On activation with catalytic amounts of gold(I) complexes, 3-silyloxy 1,6-enynes can react through two alternative pathways. In one, a cascade reaction consisting of carbocyclization and subsequent pinacol rearrangement takes place. In the second pathway, a heterocyclization is followed by a Claisen rearrangement. The reaction outcome differs depending on the substitution pattern of the 3-silyloxy 1,6-enynes and, more importantly, the electronic properties of the gold-bound phosphane ligand.

Gold(I)-catalyzed Tandem Cyclization of 3-(tert-Butoxycarbonyloxy)-1,6-enynes

“…5 We first reasoned that the introduction of this substituent onto the oxygen would suppress the formation of 3 (path B, Scheme 2), because of the reduced bacisity of t-Boc group. Unlike our previous studies, 3,4 pathway A would prevail in this case. Moreover, this new catalytic reaction will provide synthetically useful cyclohexane-1,2-diol compounds possessing exo-olefins at the 4-position (2, in Scheme 1).…”

“…4 These examples indeed illustrate that the reactivity of 3-alkoxy-1,6-enynes in the divergent pathway can be controlled by the subtle variation of the substituents on the alkoxy group. In an effort to expand the scope of the catalytic reactions associated with the 3-alkoxy-1,6-enynes, we pursued further variation of the alkoxy moiety.…”

“…3 Further investigation of 3-siloxy-1,6-enynes led to the development of unprecedented gold(I)-catalyzed divergence between pinacol-terminated vs. Claisen-terminated cyclization cascades. 4 These examples indeed illustrate that the reactivity of 3-alkoxy-1,6-enynes in the divergent pathway can be controlled by the subtle variation of the substituents on the alkoxy group. In an effort to expand the scope of the catalytic reactions associated with the 3-alkoxy-1,6-enynes, we pursued further variation of the alkoxy moiety.…”

Gold(I)‐Catalyzed Synthesis of Highly Substituted 2‐Cyclopentenones from 5‐Siloxypent‐3‐en‐1‐ynes

“…(1)]. [6,7] A remarkable feature of this reaction is that even poorly reactive Osilyl ethers can add efficiently to the alkynes in the presence of cationic gold(I) complexes. [8] In an effort to extend the scope of the reactions initiated by this intriguing siloxycyclization, we considered a catalytic reaction of 5-siloxypent-1-ynes 1 (Scheme 1).…”

Gold‐Catalyzed Addition of Oxygen Nucleophiles to CC Multiple Bonds

“…The course of the gold(I)-catalyzed cyclization of 3-silyloxy-1,6-enynes depends on the nature of the supporting ligand. For example, treatment of 3-silyloxy-1,6-enynes with a catalytic amount of [P(t-Bu) 2 o-biphenyl]AuCl/AgSbF 6 leads predominantly to tandem carbocyclization/pinacol rearrangement to form methylene cyclopentane whereas reaction of 3-silyloxy-1,6-enynes with a catalytic amount of [P(C 6 F 5 ) 3 ]AuCl/AgSbF 6 leads to tandem carbocylization/Claisen rearrangement to form 4-cycloheptenone [89]. [P(C 6 F 5 ) 3 ]AuCl (1 mol %) AgSbF 6 (1mol %) OMe OMe ð12:28Þ…”