Gold(i)-catalyzed cycloisomerization of vinylidenecyclopropane-enes via carbene or non-carbene processes

Abstract

Gold catalyzed cycloisomerization of aromatic ring tethered vinylidenecyclopropane-enes provides a divergent synthetic protocol for the construction of O-containing fused heterocycles through controllable carbene or non-carbene related processes.

C(sp3)−H Functionalizations Promoted by the Gold Carbene Generated from Vinylidenecyclopropanes

“…The outcomep rovides partial support that the On the basis of above deuterium-labeling experiment and our previousw ork, [9] ap lausible mechanism for this gold-catalyzed C(sp 3 )ÀHb ond functionalization has been outlinedi n Scheme 3. The outcomep rovides partial support that the On the basis of above deuterium-labeling experiment and our previousw ork, [9] ap lausible mechanism for this gold-catalyzed C(sp 3 )ÀHb ond functionalization has been outlinedi n Scheme 3.…”

“…Recent-ly,w eh ave reportedt hat vinylidenecyclopropanes (VDCPs) could generate in situ ag old carbene species under gold catalysis due to their amphiphilic characters, and this carbene intermediate could be trapped by an intramolecular CÀCd ouble bond of an allyloxy or homoallylic group to give fused heteroor carbocyclicp roducts in good yields. [9] Thus, we envisaged that this in situ generated gold carbene could demonstrate its intramolecular CÀHb ond insertion ability throughd elicate designo fasubstrate structure. The realization of this process could therefore expand the reactivity of this new gold carbene species generated from VDCPs.…”

“…Gold carbenes derived from diazo compounds, [5] enyne cycloisomerization, [6] dual-gold catalysis, [7] and oxidation of alkynes [8] have been extensively investigated in this fieldand have achieved great progress (Scheme 1). [9] Consideringt he acidity of the C(sp 3 )ÀHb ond would influence the reaction outcome, we used para-chloridesubstituted molecule 1'' as as ubstrate. [9] Thus, we envisaged that this in situ generated gold carbene could demonstrate its intramolecular CÀHb ond insertion ability throughd elicate designo fasubstrate structure.…”

Functionalized Benzofurans via Microwave‐Promoted Tandem Claisen‐Rearrangement/5‐endo‐dig Cyclization

“…We started the investigation into the microwave‐promoted tandem sequence with precursor 4a , which was synthesized from 2‐allyloxybenzaldehyde ( 1a ) in two steps via carbonyl alkynylation using the Bestmann–Ohira reagent 2 , followed by Sonogashira coupling of 3a with iodobenzene. For the latter step, the copper‐free reaction conditions published by Liang et al were used (Scheme ).…”

Gold(I)‐Catalyzed Cycloisomerization of ortho‐(Propargyloxy)arenemethylenecyclopropanes Controlled by Adjacent Substituents at Aromatic Rings

“…Next, ring enlargement of intermediate B affords intermediate C,w hich forms intermediate D by intramolecular cyclopropanation [18] and methylenecyclopropane migration via three-membered ring transition state TS3 (Scheme 7). [12e, 19] Intermediate G,l ikely having some gold carbenoid character, [20] is ar esonance structure of intermediate F.T hen the Oa toma ttacks the cyclobutenyl cation to give the correspondingp ropargylic ether oxonium ylide [21] intermediate H, which undergoes the corresponding [2,3]-sigmatropic rearrangement [22] by CÀOb ond cleavage (O1'ÀC1), CÀCb ond formation( C2'ÀC3), ands imultaneous dissociation of the gold catalysttog ive the final product 4d. In Cycle II, the gold complex initially activates the double bond of methylenecyclopropane to produce intermediate E,w hich rearranges to the corresponding cyclobutenyl cationic intermediate F throughr ing enlargement.…”