Catalytic Copper-Mediated Ring Opening and Functionalization of Benzoxazoles

Abstract

A novel reaction involving benzoxazole, ethyl diazoacetate, and water has been discovered, with TpBr3Cu­(NCMe) (TpBr3 = hydrotris­(3,4,5-tribromopyrazolyl)­borate) as the catalyst. The fused azoles are converted into highly functionalized substituted benzenes bearing aldehyde, amine carboxylate and hydroxyl groups. The protocol has been applied for a series of benzoxazoles with several diazo compounds. Experimental data and theoretical calculations have led to a mechanistic proposal that includes carbene addition, ylide formation, and water addition to the latter, all those steps being catalyzed by the copper center.

Copper–Carbene Intermediates in the Copper‐Catalyzed Functionalization of OH Bonds

“…Geometry around the metal center is trigonal planar,a tv ariance with that in 2a,i nw hich the k 3 coordination of the Tp Ms ligand ensures at etrahedral geometry.T herefore, complex 2a is the first example of a h 1 -N-diazoc ompound adduct in such an environment. The Pheda ligand behaves as a s-donor ligand without significant contribution of p-back-bonding from the metal to the diazoalkane ligand, [12] as inferred from the structurald ata:t he N(7)-N(8) [1.1371 (18) ] and N(8)-C(38) [1.322 (2) ] bond lengths and the N(7)-N(8)-C(38) angle [178.59 (17) 8]f or 2a are comparable to the corresponding values found for free phenyldiazoacetates,afeature also observed in the trigonal planar complexes mentioned above.A sf or [{Ph 2 B(CH 2 PtBu 2 ) 2 }Cu{h 1 -N 2 CMes 2 }],t he N(8)-N(7)-Cu(1) angle slightly deviates from linearity [161.17(13) 8]. Nevertheless, these data show that both N(7) and N(8) present sp hybridization (see the Supporting Information for full description of the crystal structure).…”

Assembly of a mononuclear ferrous site using a bulky aldehyde-imidazole ligand

“…It is possible that chelation may be necessary to stabilize this type of bond. The C=O bond distance in 1 is 1.228(4) Å which is long compared to the same distance in uncoordinated aldehydic carbonyl groups [56,57]. This lengthening is due to donation of electron density by O1 to the Lewis acidic iron center.…”

Ytterbium(III) Trifluoromethanesulfonate Catalyzed Ring‐Opening C(sp3)−N Bond Formation of Benzoxazoles with Propargylic Alcohols

“…reported a ring‐opening C(sp 3 )−N bond formation reaction of benzoxazole with diazo compounds in the presence of Tp Br3 Cu(NCMe) (Tp Br3 =hydrotris(3,4,5‐tribromopyrazolyl)borate, NCMe=acetonitrile) as the catalyst for the first time [Scheme , Eq. (4)] . However, the use of the nonavailable Tp Br3 Cu(NCMe) catalyst and dangerous diazo compounds has restricted applications of this reaction.…”

“…(4)]. [9] However,t he use of the nonavailable Tp Br3 Cu(NCMe) catalysta nd dangerous diazo compounds has restricted applications of this reaction. Herein, we describe an unprecedented ytterbium(III) trifluoromethanesulfonate [Yb(OTf) 3 ]catalyzed ring-opening C(sp 3 )ÀNb ond formationr eaction of benzoxazole with propargylic alcohols [Scheme 1, Eq.…”