Alkoxy groups, secondary

With the exception of adamantane and few related compounds [1-5] in which dichlorocarbene reacts at the tertiary C-H centre, the yields for the majority of insertion reactions into hydrocarbons are low and of little synthetic value (Table 7.1). Reaction also occurs in low yield at benzylic C-H sites [1, 6, 7] and, in the case of simple alkanes, the insertion reaction is promoted by alkoxy groups [1,6-14], Thus, whereas methylcyclohexane produces only 4% yield of the l-dichloromethyl-l-methylcyclohexane, the corresponding yield with 1-methoxycyclohexane is 13% [6], Similarly, the low yielding reaction of 1-methoxyadamantane with dichlorocarbene produces l-dichloromethyl-3-methoxyadamantane by insertion into the tertiary C-H site and (2,2-dichioroethoxy)adamantane by reaction at the primary C-H site, which is activated by the methoxy group. No reaction occurs at the secondary C-H sites [2],... 

In the case of the alkenylhthium derived from the secondary (E)-y-iodo allylic ether 219, in which chelation of the metal by the alkoxy group could no longer operate, the allylzincation led after hydrolysis to 220 as a 76/24 mixture of anti and syn diastereo-mers. The stereochemical outcome was rationalized by assuming that the conformational... 

The Corey group has reported that Cp2TiCl2/nBuLi effectively catalyzes the high yield alcoholysis of primary, secondary, and tertiary silanes with a variety of alcohols under mild reaction conditions.160 All Si-H functionalities are replaced with alkoxy groups in reactions of ethanol and phenol, although increased temperatures and/or reaction times are required for highly substituted hydrosilanes. The system also appears to be influenced... 

Chemically, the triarylmethane dyes are monomethine dyes with three terminal aryl systems of wind] one or more arc substituted with primary, secondary, or tertiary amino groups or hydroxyl groups in the para position to the methine carbon atom. Additional substituents such as carboxyl, sulfonic acid, halogen, alkyl, and alkoxy groups may be present on the aromatic rings. The number, nature, and position of these substituents determine both the hue or color of the dye and the application class to which the dye belongs. 

It was shown recently that the phenoxy group in the l-aryl-5-phenoxytetrazoles is relatively easily (NaOH, 60 °C, 0.5 h) replaced by alkoxy groups upon treatment with primarily or secondary aliphatic alcohols. The corresponding l-aryl-5-alkoxytetrazoles are formed in 59-78% yields <2000RJ01698>. 

If we treat alkoxycarbcne complexes not with phosphines but with primary or secondary amines, we observe a new kind of reaction, reminiscent of the reactions of esters. This observation led us into peptide chemistry along a path that proved to be quite surprising to a coordination chemist. We could show that the alkoxy group of alkoxy(organo) carbene complexes can be substituted not only by mono- or dialkylamino residues but also by free amino groups of amino acid and peptide esters (63, 64). The principle of this reaction is shown in Scheme 2. 

This mechanism was supported by the experimental facts that the acetals of primary alcohols were less completely converted than those of secondary alcohols, because the equilibrium shown in eq. 13.2 will be less favorable for the formation of unsaturated ether when the alkoxy groups are primary. Acetals may also be hydrogenolyzed in a neutral solvent over a palladium catalyst not containing alkali.9,10... 

In the second classical method (Bischler synthesis), an aromatic primary or secondary (arylalkyl, but not diaryl) amine is condensed with an obromo (or better, hydroxy) ketone to give a 2,3-dialkylindole. This in turn is alkylated directly to the 1,2,3,3-tetraalkylindoleninium salt. Use of acetoin gives 2,3-dimethylindole, which is easily isolated and purified. The Bischler synthesis from a substitued aniline, and especially from anilines bearing one or more alkoxy groups, is much preferred in practice for indoles substitued in the 4-7-positions, since the substituted aiylhy-drazines needed for the Fischer synthesis are costly, unstable, or unavailable. 

By treatment of alkoxymethyleneiminium salts or alkylmercaptomethyleneiminium salts with primary or secondary amines the alkoxy group or the alkylmercapto group, respectively, is replaced by the amino group forming amidinium salts (137 Scheme 16). The byproducts, alcohols or thiols, are easy to remove by distillation in vacuo. Especially in the case of alkoxymethyleneiminium salts it is necessary for the reaction temperature to be as low as possible to suppress the competing dealkylation of the salt (138) by the amine giving rise to ammonium salt formation. 

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