Phenol, ruthenium-catalyzed alkylation

The pioneering study of ruthenium-catalyzed regioselective alkylation using olefins as an alkylating reagent was reported by Lewis and Smith [24]. The ortho-selective ethylation of phenols with ethylene can be attained with the aid of a ruthenium(II) phosphite complex as a catalyst. This alkylation takes place exclusively at the position ortho to the hydroxyl group, and the corresponding 1 2 addition product is the major product (Eq. 6). The use of potassium phe-noxide is the key in this catalytic reaction. Unfortunately, however, the applicability of this reaction is narrow. Thus, phenol is the only applicable substrate in this reaction. 

Stoichiometric cycloruthenation reactions, as well as the early example of catalytic deuteration of phenol (see above) [38] served for the development of efficient catalytic strategies for C-C bond formations through C-H bond functionalizations. Indeed, ruthenium-catalyzed atom-economical [51] addition reactions of arenes onto C-C multiple bonds, hydroarylations [52-57], were found to be very useful. In an early example, Lewis and Smith disclosed a regioselective alkylation of phenol through in situ formation of its phosphite, and subsequent directed C-H bond functionalization (Scheme 8) [58],... 

Several other mechanistically distinct metal-catalyzed dearomatization procedures have been reported, and almost all involve phenol or naphthol derivatives undergoing dearomatization via intramolecular transformations. Intramolecular Pd- and Rh-catalyzed C4-arylation and alkylation of /)ara-substituted phenols has been used to construct compounds of general structure 82 (Fig. 15.1) [86]. These reactions rely on generation of electrophilic aryl or alkyl o-metal complex intermediates that participate in tandem C4 metalation-reductive elimination with an attached phenol. Ruthenium- and Pt-catalyzed reactions of naphthalenes and alkynes deliver spirocyclic products such as 83 [87, 88]. An asymmetric intramolecular naphthalene dearomatization catalyzed by Pd(0)-phosphine complexes has been used to prepare carbazole derivatives 84 in good enantiomeric excess from l-(AI-2-bromophenyl)aminonaphthalene precursors [89]. 

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