Phenyl transfer

Forward, J.M., Fackler, J.P. and Staples, R.J. (1995) Synthesis and structural characterization of the luminescent Gold(I) Complex [(MeTPAJjAulJIj. Use of NaBPha as a phenyl transfer reagent to form [(MeTPA)AuPh](BPh4) and (TPA) AuPh. Organometallics, 14, 4194—4198. 

Aryl zinc reagents are considerably more reactive than alkylzinc reagents in these catalyzed additions to aldehydes.151 Within the same computational framework, phenyl transfer is found to have about a lOkcal/mol advantage over ethyl transfer.152 This is attributed to participation of the tt orbital of the phenyl ring and to the greater electronegativity of the phenyl ring, which enhances the Lewis acid character of the catalytic zinc. 

An important issue was the fact that isolated diphenylzinc had to be used in this protocol and that samples of this arylzinc reagent prepared in situ (and presumably still containing lithium or magnesium salts) led to products with lower enantioselectivities. Thus, although pure diphenylzinc was commercially available, its high price was expected to hamper large-scale applications of this catalyzed asymmetric phenyl transfer process [36, 37]. 

With the aim of improving understanding of the mechanism of the ferrocene-catalyzed aryl transfer reactions from organozincs to aldehydes, DPT calculations were performed in close collaboration with Norrby [64]. As a result, the experimentally observed higher reactivity of the phenyl transfer to aldehydes compared... 

For the application of this phenyl transfer protocol by others using different catalysts, see a) G. Zhao, X.-G. Li, X.-R. Wang, Tetrahedron Asymmetry... 

For a recent report on the application of this phenyl transfer protocol using a proline-derived catalyst with dendritic polyether wedges, see X. y. Liu, C. y. 

Substituted [2.2]Parac fciopbane Derivatives as Efficient Ligands 211 Table 2.1.3.2 Substrate spectrum for the phenyl transfer to imines. ... 

Dosa and Fu reported the first catalytic enantioselective phenyl transfer reaction to ketones (equation 25)100. In the presence of 1.5 equivalents of MeOH, the chiral tertiary alcohol was produced in good yield and with high enantioselectivity. Walsh and workers recently reported the Ti(OE -i Vchiral dihydroxybis(sulfonamide) catalyst 34 system, whereby enones have been converted to enantioenriched allyl alcohols101. 

A Lewis base ligand has been developed as the chiral catalyst. Dahmen, Brase and coworkers reported that the [2.2]paracyclophane-based chiral N,O-ligand 8 (2 mol%) affords (V-formylamine with 84-95% (equation 34)134. In this system, the phenyl transfer reaction also proceeds in a catalytic manner134b. 

Chiral diarylmethanols have been prepared enantioselectively by phenyl transfer to benzaldehydes, using PhB(OH)2-ZnEt2 and a new tertiary aminonaphthol auxiliary.246... 

Also [AuPh(TPA)] (TPA = l,3,5-triaza-7-phosphaadamantane) is obtained in a similar phenyl-transfer reaction using Na[BPh4] and [Au(TPA)3]C123 [Eq. (3)]. Although the [BPh4] anion is well known for participating in phenyl-transfer reactions with other transition metals,24 these appear to be the first reported examples of phenyl transfer to a gold center. 

These types of compounds are scarcely represented due to the low number of cationic ligands available and no general method for their synthesis exists. One example is [AuPh(MeTPA)]BPh4, which contains the cationic ligand MeTPA+, derived from 1,3,5-triaza-7-phosphaadamantane, synthesized through an unusual phenyl-transfer reaction in aqueous solution [Eq. (12)].23... 

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