Catalytic palladium-oxyallyl cycloaddition

Abstract

Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.

Catalytic Domino Annulations through η3‐Allylpalladium Chemistry: A Never‐Ending Story

“…Very recently, the group of Trost extended the use of zwitterionic dipoles to oxyallylpalladium cations generated from silyloxyallylcarbonates . By mixing these highly reactive species with linear or cyclic dienes, various tetrahydrofuran derivatives could be efficiently prepared via a [3+2]‐cycloaddition procedure (Scheme , Equation 1).…”

DFT Study on the Gold(I)‐Catalyzed Dehydrogenative Heterocyclization of 2‐(1‐Alkynyl)‐2‐alken‐1‐ones to form 2,3‐Furan‐Fused Carbocycles: Effects of Additives C5H5NO vs. PhNO

“…Recently, the transition‐metals have been widely employed to promote the synthesis of substituted furans as catalysts under the mild reaction conditions . For instance, Trost et al disclosed a successful catalytic (3 + 2) cycloaddition involving Pd‐oxyallyl species to yield a diverse range of cis‐fused methylene tetrahydrofurans . Qi and co‐workers reported that a cascade reaction to synthesize spirocyclopenta[c]furans by using a single gold catalyst (Ph 3 PAuNTf 2 ) realizes the synergistic activation of two substrates in one pot, in which three rings were constructed efficiently with multiple bond cleavages and formation under mild conditions .…”

“…[19][20][21][22] For instance, Trost et al disclosed a successful catalytic (3 + 2) cycloaddition involving Pd-oxyallyl species to yield a diverse range of cis-fused methylene tetrahydrofurans. [23] Qi and co-workers reported that a cascade reaction to synthesize spirocyclopenta[c]furans by using a single gold catalyst (Ph 3 PAuNTf 2 ) realizes the synergistic activation of two substrates in one pot, in which three rings were constructed efficiently with multiple bond cleavages and formation under mild conditions. [24] El Arba et al demonstrated a novel Ru (II)-catalyzed conversion of vinyl diazoesters to trisubstituted and tetrasubstituted furans that proceeded under mild reaction conditions with broad substrate scope.…”

Catalytic (3+2) Palladium‐Aminoallyl Cycloaddition with Conjugated Dienes

“…[5] In 2018, we demonstrated that tailored oxyallyl precursors with an electron-withdrawing group could participate in the Pd-catalyzed (3+ +2) cycloaddition with conjugated dienes to afford various fused or highly substituted tetrahydrofuran rings (Scheme 1B,Eq. [6] Thec ycloaddition is proposed to override the conventional (4+ +3) chemoselectivity of oxyallyl cations through aPd-allyl transfer/ring closure sequence,a nd the pendant electronwithdrawing group proved indispensable for inhibiting the formation of af our-membered palladacycle that leads to the (2+ +1) cyclopropanation product. [6] Thec ycloaddition is proposed to override the conventional (4+ +3) chemoselectivity of oxyallyl cations through aPd-allyl transfer/ring closure sequence,a nd the pendant electronwithdrawing group proved indispensable for inhibiting the formation of af our-membered palladacycle that leads to the (2+ +1) cyclopropanation product.…”

“…Nevertheless,while the reaction of an oxyallyl precursor with linear dienes was able to proceed at 90 8 8C, [6] the Pdaminoallyl cycloaddition requires an elevated temperature (110 8 8C). Dienes containing functional groups that have distinct electronic properties can all participate in the reaction to give 2-alkylidene-5-vinyl-pyrrolidines (9m-9s).…”