O-H bond arylations

Figure 4.1 Copper-mediated cross-coupling concepts for O—H bond arylation.

Discovery and Development of a New O—H Bond Arylation Reaction From Stoichiometric to Catalytic in Copper... 

I 4 Copper-Catalyzed Arylations of Amines and Alcohols with Boron-Based Arylating Reagents Table 4.1 Stoichiometric and the first catalytic O—H bond arylation. 

A systematic study for boronic acid replacements for N—H bond arylations has been investigated, and the outcome compares favorably to the O—H bond arylation reaction (Table 4.6) [17,41]. However, to date no catalytic in copper variations have been reported with these alternative aryl donors. The best donors are triarylborox-ines and boronic acid esters derived from 2,2 -dimethyl-l,3-propanediol and 1,3-propanediol and, as in the case of the O—H bond arylation, the pinacolate esters are poor aryl donors. Sodium tetraphenylborate is also an alternative phenyl donor in the copper] 11)-mediated, microwave-assisted N-arylation using KF-AI2O3 as heterogeneous base in the absence of solvent [30]. 

The use of potassium aryltrifluoroborate salts as useful bench-stable alternatives to arylboronic acids has been demonstrated in O—H bond arylations (vide supra),... 

The use of Mn-salen catalysts for asymmetric epoxidation has been reviewed.30 Oxo(salen)manganese(V) complexes, generated by the action of PhIO on the corresponding Mn(III) complexes, have been used to oxidize aryl methyl sulfides to sulfoxides.31 The first example of C—H bond oxidation by a (/i-oxo)mangancsc complex has been reported.32 The rate constants for the abstraction of H from dihydroanthracene correlate roughly with O—H bond strengths. 

In the presence of a ruthenium catalyst, 3-diazochroman-2,4-dione 716 undergoes insertion into the O-H bond of alcohols to yield 3-alkyloxy-4-hydroxycoumarins 717 (Equation 285) <2002TL3637>. In the presence of a rhodium catalyst, 3-diazochroman-2,4-dione 716 can undergo insertion into the C-H bond of arenes to yield 3-aryl-4-hydroxy-coumarins (Equation 286) <2005SL927>. In the presence of [Rh(OAc)2]2, 3-diazochroman-2,4-dione 716 can react with acyl or benzyl halides to afford to 3-halo-4-substituted coumarins (Equation 287) <2003T9333> and also with terminal alkynes to give a mixture of 477-furo[3,2-f]chromen-4-ones and 4/7-furo[2,3-3]chromen-4-ones (Equation 288) <2001S735>. 

These iminosilanes react with H-acid compounds like water and ethanol by insertion into the O-H bond, with acetone and 2,3-dimethyl-1,3-butadiene to give alkenes, and with methacrolein, ethylvinylether, silyl and aryl azides to give cycloadducts. 

The presence of any of several functional groups is likely to impart photolability to drug molecules. These include carbonyl (C=0), nitroaromatic, -N-oxide, -alkene (C=C), aryl chloride, weak C-H and O-H bonds, sulfides, and polyenes. Some of these functional groups impart photolability as a result of their chromophoric properties (e.g., carbonyl) and some of them impart photolability by virtue of their weak covalent bonds, (e.g., O-H bonds). A list of several common bonds and their respective bond energies (E ) and the corresponding wavelengths ( ) are presented in Table 1. 

Emboldened by methodological advances, theoreticians began to apply their toolchests to quite a few more CH- - -X systems in the 1990s [118 121]. One of the earliest studies that examined a system with direct biological significance appeared in 1993 wherein Feller and Feyereisen [122], examined the CH- - -O interaction between an aryl CH of phenol (a possible model of the Tyr side chain) and the O of water. However, analysis of this interaction was hampered as it was weaker than, and secondary to, the more conventional OH- - -O H-bond between the same two molecules. 

The catalyst Cu/(S S,S)-23a was also efficient for the insertion of O—H bonds of phenols (Scheme 44) [109], Under similar conditions as that for N—H insertion reactions, a wide range of phenol derivatives underwent O—H bond insertion with a-diazopropionates, providing a-aryloxypropionates with excellent enantioselectivities (95-99.6% ee). The Pd/(S, S,5 )-23a-catalyzed asymmetric O—H bond insertion reaction between a-aryl-a-diazoacetates and phenols provided the first enantioselective method for the preparation of chiral a-aryloxy-a-arylacetates, which are ubiquitous in biologically active molecules (Scheme 45) [110]. 

With IB hgating to Rh2(OAc)4 to form a chiral catalyst for inducing insertion of methyl aryl(diazo)acetate into the O-H bond of a benzy lie alcohol, it also enables further addition of the product into an aldimine. Both reactions are rendered as5munetric. ... 

In the past, copper acetate has been the most popular choice of catalyst for many O—H and N—H bond arylation reactions, although it is not exclusive. The use of catalytic amounts of copper]I) oxide offers a valuable alternative and a range of azoles, anilines and aliphatic amines, all used in slight excess, can each be efficiently functionalized using the ophmized protocol (Scheme 4.22), where air as a co-oxidant is essential (60). 

Although not a direct N—H bond arylation, a related new reductive protocol for the amination of arylboronic acids has been developed which utilizes nitroso arenes. This reaction is certainly worthy of inclusion here, as it broadens our understanding of the cross-coupling processes of heteroatom-carbon bonds via N—O bonded species [61]. These new protocols rely on either stoichiometric amounts of CuCl (Scheme 4.23) or on catalytic amounts of copper(II) methylsalicy-late (CuMeSal) (Scheme 4.24). The need for stoichiometric amounts of a copper(I)... 

Abstract The selective catalytic activation/functionalization of sp C-H bonds is expected to improve synthesis methods by better step number and atom economy. This chapter describes the recent achievements of ruthenium(II) catalysed transformations of sp C-H bonds for cross-coupled C-C bond formation. First arylation and heteroarylation with aromatic halides of a variety of (hetero)arenes, that are directed at ortho position by heterocycle or imine groups, are presented. The role of carboxylate partners is shown for Ru(II) catalysts that are able to operate profitably in water and to selectively produce diarylated or monoarylated products. The alkylation of (hetero)arenes with primary and secondary alkylhalides, and by hydroarylation of alkene C=C bonds is presented. The recent access to functional alkenes via oxidative dehydrogenative functionalization of C-H bonds with alkenes first, and then with alkynes, is shown to be catalysed by a Ru(ll) species associated with a silver salt in the presence of an oxidant such as Cu(OAc)2. Finally the catalytic oxidative annulations with alkynes to rapidly form a variety of heterocycles are described by initial activation of C-H followed by that of N-H or O-H bonds and by formation of a second C-C bond on reaction with C=0, C=N, and sp C-H bonds. Most catalytic cycles leading from C-H to C-C bond are discussed. 

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