Abstract
Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]2 and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i.
Highlights
The use of oxabicyclic templates to introduce trans-1,2-bifunctional groups to the carbocyclic molecule skeleton is an effective strategy for the synthesis of complex molecules
Pioneering work in this field was first described by Lautens and co-workers [1–17] who reported rhodium-catalyzed asymmetric ring-opening (ARO) of oxabicyclic alkenes to produce the corresponding products in high yields and excellent enantioselectivities
Cheng et al [56–59] recently described asymmetric ring-opening of oxabenzonorbornadiene with alkyl- or alkenyl- or allylzirconium reagents and zinc powder under mild conditions catalyzed by Ni(dppe)Br2 or Pd((R)-binap)Cl2, which yielded the corresponding 1,2-dihydronaphth-1-ols in good to excellent yields with high enantioselcetivities
Summary
The use of oxabicyclic templates to introduce trans-1,2-bifunctional groups to the carbocyclic molecule skeleton is an effective strategy for the synthesis of complex molecules Pioneering work in this field was first described by Lautens and co-workers [1–17] who reported rhodium-catalyzed asymmetric ring-opening (ARO) of oxabicyclic alkenes to produce the corresponding products in high yields and excellent enantioselectivities (up to 99% ee). Cheng et al [56–59] recently described asymmetric ring-opening of oxabenzonorbornadiene with alkyl- or alkenyl- or allylzirconium reagents and zinc powder under mild conditions catalyzed by Ni(dppe)Br2 or Pd((R)-binap)Cl2, which yielded the corresponding 1,2-dihydronaphth-1-ols in good to excellent yields with high enantioselcetivities (up to 90% ee). Our group demonstrated that iridium-catalyzed asymmetric ring-opening of oxaand azabicyclic alkenes with nitrogen- or oxygen-based nucleophiles, such as amines, alcohols, phenols. Cdoifnfseerqenuet ntytlpye, sa omfocrheireafflicliigeannt idrsidrieuamctecadtawlyitsht s[yIrs(tCemODfo)rCl]2 to fothrme rinrigd-oiupmencinogmrpealecxtieosntwoadseetxeprmloirnede.tThheevdiaifbfeilrietnytotyf pthees oefncahnitriaolsleigleacntdivsirteyac(Stecdhewmiteh 1[I)r.(CToOpDr)oCbl]e2 the iridituomfo-rcmatiarlidyziuemd acsoymmpmlexeetsritcordinegte-rompienneinthgeovfiaobxialibtyicoyfctlhiceaelnkaennteio1saelwecittihvi1ty-((2S-cflhueomreop1)h.eTnoypl)rpoibpeetrhaezine, chiriarildbiuismp-hcaotsaplyhziendealsiygmanmdet(rSic)-rpin-Tgo-ol-pBeInNinAg Pofwoxaasbuicsyecdlicaanlkden1ee1qauwiviathle1n-(t2o-ffluNorHop4Ihewnaysl)paidpdereadzinaes, the addcihtiivrael. bWisephfoosupnhdintehlaitgathned r(iSn)-gp--oTpoel-nBiInNgApProwdauscuts2ead wanads 1obetqauiniveadleinnt hofigNhHy4iIewldas(uapddtoed99a%s t)hwe ith modaderdaittievee.nWanetifoosuenledctthivaittyth(e54ri%nge-eo)p(eTnaibnlge p1r,oednutrcyt 24a).wHaoswobetvaeinr,etdheinehniagnhtiyoimelder(iucpextoce9s9s%v)awluiethwas lowm(2o%de–r5a8t%e eenea)nwtihoseenle(cSt)i-vBitIyN(A54P%aened) (fTearbrolece1n, eenbtirsyp4h)o. sHpohwineevelirg, athnedesnwanetrieomuseerdicaesxcthesescvhailruael lwigaasnds (Tabl(oTlewab1(l,2ee%1n,–t5erin8e%tsri1eee–s)31w)–.h3T)e.nhTe(hSee)n-eBanInNatnAitoiPmomaenerdircifceeerxrxcocecesessns evvaballiuuspeehwwosaapssh55i5n5%e%leieegeawnwhdhesnewn(Se(r)S-ep)u--Tps-eoTdl-oBals-INBthIANePcAhwPiraawsl ulaisgseaudnsdaessd as the tlhigealnigdanind tihnethperepsreensecnecoefo1f.12.52%5%mmool l[I[rIr((CCOODD))CCll]]22 ((TTaabbllee11, ,eenntrtyry5)5.)T. hTehreerfoerfeo,r(eS,)(-Sp)-T-po-lT-BoIlN-BAINP AP waswcahsocsheonsaens tahsethoepotipmtiimzeizdedligliagnadnd
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