Aldehyde group, introduction into

Reimer-Tiemann Reaction. —Both the ortho- and para-hydroxy benzaldehydes are important. They may both be synthesized by what is known as the Reimer-Tiemann reaction. This consists of the interaction between a salt of a phenol and chloroform in the presence of an excess of alkali. The result is the introduction of the aldehyde group, (—CHO), into the benzene ring of the phenol as follows ... 

The acetylacetonates of chromium, cobalt, and rhodium were found to react with dimethylformamide in the presence of phosphorus oxychloride to yield formyl-substituted chelates (10). This is a well known technique for the introduction of an aldehyde group into reactive aromatic systems. The formylation of the chelate rings is a slow reaction, and by controlling the conditions it is possible to... 

The conversion of an a, -unsaturated aldehyde or ketone into an allylic acetal or ketal, followed by SN2 -type attack of a nucleophile, leads, after hydrolysis of an initially formed enol ether, to a fi-sub-stituted carbonyl compound. The overall sequence (Scheme 23) is equivalent to a direct conjugate addition, but has the advantage that it allows the temporary introduction of a chiral auxiliary group if a chiral (C2-symmetric) diol is used in the acetalization step, die subsequent nucleophilic addition leads to a mix-... 

There are several methods for the direct introduction of an aldehyde group into an aromatic compound. In the Vilsmeier-Haack reaction, activated aromatic systems such as aryl ethers and dialkylanilines are formylated by a mixture of dimethylformamide, HCONMe2, and phosphorus oxychloride, POCL, (Scheme 6.4). The process involves elec-trophilic attack by a chloroiminium ion, Me2N=CHCl, formed by interaction of dimethylformamide and phosphorus oxychloride. Hydrolysis of the dimethyl imine completes the synthesis. 

Introduction of the aldehyde group into ar. nuclei according to Reimer-Tiemann H —CHO... 

Fetuin. — After introduction of aldehyde groups at C-7 of neuraminic acid residues in fetuin, an amine-containing spectroscopic probe has been attached to the molecule by reductive amination. The spin-label has also been introduced into asialofetuin after modification of the glycoprotein with either D-galactose oxidase or sodium periodate. 

Perchlorobutyryl chloride Introduction of aldehyde groups into ar. rings... 

The well-known powerful basic catalyst 4-dimethylaminopyridine has been the inspiration for a new transesterification catalyst for a-hydroxy esters (5). The designer compound is 2-formyl-4-pyrrolidinopyridine (6). By the introduction of an aldehyde group into the pyridine ring at the 2-position, the ready formation from (5) of a hemi-acetal (7) makes possible, via a covalent pre-association step, a facile displacement by pyridine nitrogen of the aryloxy group of the a-hydroxy ester (5). The product of this process, a tricyclic pyridinium compound (9), is formed by a nucleophilic mechanism (Scheme 1, pathway b), and interaction with methanol then leads to the methyl ester of the a-hydroxy acid (10) and regeneration of the catalyst. However, a study of the mechanism of this catalytic process discounted the nucleophilic mechanism and provided clear evidence instead for a general base mechanism, which proceeds via a dioxolanone (8) (Scheme 1, pathway a) ... 

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