Rhodium‐Catalyzed Aryl Transfer from Trisubstituted Aryl Methanols to α,β‐Unsaturated Carbonyl Compounds

Abstract

In transition-metal-catalyzed organic reactions involving carbon-carbon bond formation, a carbon-metal catalyst bond is often generated by transmetalation of the organic group in an organometallic reagents. For example, in the rhodium-catalyzed conjugate arylation of electron-deficient alkenes, a wide variety of arylating reagents composed of B, Si, Zn, Sn, and Ti have been used for the formation of aryl rhodium intermediates by transmetalation (Scheme 1).[1] On the other hand, it has been recently reported that organotransition-metal species can be generated from metal alkoxides through b-hydrocarbyl elimination (Scheme 2) in some catalytic organic transformations. [2][3][4][5][6][7] As for b-aryl group elimination, Miura and co-workers disclosed that the palladium-catalyzed cross-coupling of aryl halides to give biaryls proceeds with trisubstituted aryl methanols as coupling partners.[3] They also reported the palladium-catalyzed hydroarylation of enones with trisubstituted aryl methanols, although the reaction requires severe reaction conditions (xylene, 160 8C).[3c] Recently, stoichiometric b-phenyl elimination on rhodium was reported by Hartwig and co-workers, in which rhodium tert-alkoxide complexes [Rh(OCR 2 Ph)(PEt 3 ) 3 ] generate the phenylrhodium complex [RhPh(PEt 3 ) 3 ] and the corresponding ketones under mild conditions.[8] During our efforts to realize catalytic organic transformations utilizing the b-hydrocarbyl elimination process on transition-metal alkoxides, [5b, 6a-d] we found that the acridinols 1 (Bn = benzyl), which are readily obtained by Grignard addition to 10-benzylacridin-9(10H)-one (2), are highly reactive towards b-aryl elimination on their alkoxide complexes. Herein, we describe the rhodium-catalyzed conjugate arylation of a,b-unsaturated carbonyl compounds with the trisubstituted aryl methanols 1 as aryl transfer reagents.In the first set of experiments, several types of a,asubstituted benzylalcohols were examined for their reactivity in the rhodium-catalyzed 1,4-addition to 3-nonen-2-one (3 a; Scheme 3, Table 1). In the presence of [{Rh(OH)(cod)} 2 ] (cod = cycloocta-1,5-diene) as a catalyst in toluene at 110 8C for 3 h, the starting enone 3 a was recovered intact with 2-phenyl-2-propanol (4 m), triphenylmethanol (5 m), and cyclic alcohols 6 m and 7 m.[9] The reaction of xanthenol 8 m, which has been reported to be a good phenyl donor in the palladium-catalyzed cross-coupling with aryl halides, [3a] gave the 1,4-addition product 9 am, but its yield was low (22 %; Table 1, entry 1). Acridinol 1 m was found to be much more reactive than the others towards the present rhodiumcatalyzed 1,4-addition to give 9 am in quantitative yield (Table 1, entry 2). The eliminated ketone, acridinone 2, was recovered in high yield (86 %). Scheme 1. Rhodium-catalyzed 1,4-addition of aryl organometallic reagents.Scheme 2. b-Hydrocarbyl elimination.Scheme 3. Rhodium-catalyzed conjugate arylation of a,b-unsaturated carbonyl compounds through b-aryl elimination.

Rh-catalyzed asymmetric 1,4-addition reactions to α,β-unsaturated carbonyl and related compounds: an update

“…The stereoselective type of the reaction confirmed it to be highly susceptible to the electronic properties of the heteroaryl substituents, with boronates bearing electron-rich residues affording only moderate chemical yields but constantly high enantiomeric excesses (Scheme 153, Table 95). 277 A highly regio-and enantioselective Rh-catalyzed 1,4-addition of arylboronic acids 2 to b,c-unsaturated-a-ketoamides 288a utilizing a simple novel chiral sulfinylphosphine ligand L77 has been reported. Using this protocol, excellent chemo-, regio-and enantioselectivities in high yields (up to 93%) and excellent enantiomeric excess (up to 99% ee) were achieved.…”

Metal-Catalyzed Carbon–Carbon Bond Cleavage of Unstrained Alcohols

“…The group of Hayashi reported the first example of rhodiumcatalyzed β-aryl elimination in the 1,4-arylation of α,βunsaturated ketones 177 with tertiary alcohols 178 in 2007. 88 The scaffold of the donor alcohol was crucial to activate the C− C(aryl) bond. While acyclic alcohols, as well as several cyclic donors used previously with palladium, remained unreactive, a 10-benzyl-9-aryl-dihydroacridin-9-ol scaffold (177) served as a selective donor to give the desired products in excellent yield (Scheme 30).…”

“…The group of Hayashi reported the first example of rhodium-catalyzed β-aryl elimination in the 1,4-arylation of α,β-unsaturated ketones 177 with tertiary alcohols 178 in 2007 . The scaffold of the donor alcohol was crucial to activate the C–C­(aryl) bond.…”

Catalytic Carbon–Carbon Bond Activation of Saturated and Unsaturated Carbonyl Compounds via Chelate-Assisted Coupling Reaction with Indoles

“…By channeling a relief of strain energy as the driving force, catalytic C–C bond cleavage methods of cyclopropane and strained cyclic ketone derivatives have been shown to be a versatile synthetic tool for constructing a variety of cyclic compounds, as exemplified by recent asymmetric synthesis of biologically active chiral organic molecules . The catalytic β-carbon elimination method has also been shown to be effective for promoting regioselective C–C bond cleavage reactions for saturated and unsaturated hydrocarbon substrates bearing oxygen functional group . Dong and co-workers recently reported a series of catalytic C–C bond activation methods that are either driven by a relief of ring stain or are accompanied by insertion and elimination reactions .…”