At benzylic position

Radicals have also been generated at benzylic positions and shown to couple with epoxides, forming an alcohol. ... 

For a method that gives good yields at benzylic positions, see Santamaria, J. Jroundi, R. Rigaudy, J. Tetrahedron Lett., 1989, 30, 4677. 

Sulfonamides are relatively acidic and their anions can serve as nitrogen nucleophiles.64 Sulfonamido groups can be introduced at benzylic positions with a high level of inversion under Mitsunobu conditions.65... 

Figure 1. Structures, with numbering and calculated A dei0c values at benzylic positions of the tetrahydro benzo-ring derivatives of PAH discussed in this chapter.

The superbases are similar in that they avoid hindered positions next to coordinating groups, and prefer to deprotonate ortho to small, powerfully inductively withdrawing OMe, or even at benzylic positions. Superbases prefer to deprotonate both 647 and 648 ortho to OMe rather than the usually more powerfully directing anilide group (Scheme 251) . ... 

Alkylation of hydroxylamine with primary halides and sulfonates is rarely used nowadays for preparation of A-alkylhydroxylamines due to the competing formation of N,N-dialkylhydroxylamines. A number of older procedures have been reported with low to moderate yields of Al-alkylhydroxylamines. Yet, in many cases the reported low yields can be attributed to workup losses during distillation and crystallization steps rather than to the polyalkylation. Use of excess of hydroxylamine in reactions with primary alkyl halides (e.g. 3) improves the yields of monoalkylation (equation 2). Most of the examples of alkylation of hydroxylamine in good yield involve a substitution of an activated halogen atom at benzylic positions as well as in haloacetamides 4 leading to alkylhydroxylamines such as 5 where dialkylation rates are lower (equation 3). 

Alkylation of aromatics at benzylic positions can also be performed. Me3SiCH2K is a highly selective reagent for this process 253... 

Appreciably high ee-values were also observed in a series of hydroxylations at benzylic positions in all cases predominantly leading to the (R)-configured alcohol [115]. With tetrahydronaphthalene as substrate the best result was obtained 72% ee, 47% yield. 

IBX allows the introduction of carbonyl groups at benzylic positions in a very efficient way, when it is used as a heated solution in fluorobenzene-DMSO (2 1).103b 104 This reaction normally does not interfere with the normal oxidation of alcohols because alcohols are oxidized under milder conditions. 

Doubly labeled haemanthamine (318) was converted in S. formosissima into haemanthidine (248) again without 3H loss. In the same two plants [l -3H l-14C]0-methylnorbelladine (343), randomly labeled with 3H at benzylic position, was incorporated into pluviine... 

As shown by the last reaction in Scheme 5.23, the metalation of benzamides is complicated by several potential side reactions (Scheme 5.24). Thus, benzamides can also undergo ortho-metalation [181, 217-222] or metalation at benzylic positions [223-225], Ortho-metalation seems to be promoted by additives such as TMEDA, and benzylic metalation can be performed selectively with lithium amide bases [217,224], which are often not sufficiently basic to mediate ortho- or a-amino metalation. If deprotonation of the CH-N group succeeds, the resulting product might also undergo cydization by intramolecular attack at the arene [214, 216] (see also Ref. [226] and Scheme 5.27) instead of reacting intermolecularly with an electrophile. That this cydization occurs, despite the loss of aromatidty, shows how reactive these intermediates are. 

Since this method allows us easily to construct structures branched at benzylic positions, it was applied to the synthesis of -arylpropionic acids, including anti-inflammatory agents. An example is the facile synthesis of ibuprofen by such an allyl-aryl coupling and subsequent oxidation (Scheme 10-8) [29]. The cross-coupling was more effective when the substrate had an electron-withdrawing group. 

The stereochemistry of acetoxylation at benzyl positions of substituted indanes and ace-naphthenes was investigated in detail [294-296]. the cis—trans ratio of diactoxylated products is significantly larger in the anodic than in chemical processes. 

The isocoumarin and the dihydroisocoumarin ring systems occur widely in nature Their synthesis by lithiation method is according to type C and involves ortho metalation of N-methyl arylcarboxamides. The organometallic compounds on treatment with electrophilic reagents such as an epoxide or allylbromide followed by hydrolysis and cyclisation furnish the dihydroisocoumarins. Bromination at benzylic position followed by dehydrobromination then gives the isocoumarins themselves. 

Three kinds of product, phenols, sec alcohols and ketones, were formed in different ratios by the attack at aromatic and side-chain C-H bonds (Table 4). No oxidation occurred at tertiary and primary carbons, not even at benzylic positions... 

Reactions at Benzylic Positions. - The catalytic oxidation, using a cobalt bromide catalyst, of 2,5-dimethylthiophen to the dialdehydeof 3-methyl-2-ethylthiophen to 2-acetyl-3-methylthiophen and l-(3-methyl-2-thienyl)-ethyl acetate, of the four isomeric methyl acetothienones to the corresponding acetylthiophencarboxylic acids, and of 2-acetoxymethylthio-phen to thiophen-2-carboxylic acid has been reported. The Wittig reaction between 2- and 3-thenyltriphenylphosphonium salts and crocetin dialdehyde has been used for the synthesis of carotenoid analogues with terminal thiophen rings. ... 

Reaction at Benzylic Positions. - The Ivanov reagent obtained... 

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