Monoaryl Natural Products

In this brief review we will generally restrict ourselves to monoaryl compounds found in woody plants of commercial interest in forestry and agriculture. Beca.use similar monoaryl compounds are often found both in wood and in bark and because there is growing interest in whole-tree utilization, as well as in the use of plant phenols and other extractives as chemicals and other technical products, we 

In the following division into classes we present the monoaryl compounds in the order of increasing number of carbon atoms in the side-chain. 

Phenol (1) has long been reported as occurring in various parts of Firms sylvestris (89-91) the wood contains 0.03%-0.12%. More recently, it was identified in Picea abies wood by GC/MS of the trimethylsilylethers of the acetone extract (48). 

In spite of the fact that dihydroxy- and trihydroxybenzene units are very common in more complex plant phenols, they have very rarely been found and, if so, in only small amounts in the free state. Catechol (2) has been found in the bark of two Populus species (53, 130) and resorcinol (3) has been identified in the heartwood of five Moms (46) species as well as in Quercus rubra wood (152).The 4-methylcatechol, which inhibits fungal growth, was isolated in the reaction zone in sapwood of Picea abies attacked by Pomes annosus (133). 

Hydroquinone (4) is more widely distributed in plants. It occurs in Ericaceae, Rosaceae, and Compositae, and is the only Cg-phenol that is of some systematic interest (71). This compound is found in leaf and bark of the pear tree, Pyrus communis (71), and in trace amounts in the heartwood of Pinus resinosa (142) 

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Monoaryl Natural Products 375 Table 7.1.2. Structures of esters, glycosides, and amides of cinnamic acids... 

Monoaryl Natural Products 389 Table 7.1.6. Structures of miscellaneous monoaryl compounds... 

Biaryl moieties are ubiquitous in natural products and pharmaceuticals [45]. Consequentially, efficient and direct synthetic protocols for the formation of biaryl molecules are highly desirable. The earliest report of chelate-assisted C-H arylation from 1998 describes the use of Wilkinson s catalyst [RhCl(PPh3)3] for the ortho-C-H functionahzation of 2-arylpyridines with tetraphenylstan-nane (Scheme 23.13) [46]. Monoarylated products can be obtained by using a blocking group on one of the ortho positions on the pyridine moiety of the substrate (13) that prevents arylation of the second ortho-C-H bond. In the absence of a blocking substituent in the substrate 14, diarylated products are formed. 

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