Replacement, aldehyde group reaction

The oxygen of ketone and aldehyde groups is readily replaced by halogen under the influence of phosphorus trichloride or pentachloride the reaction may be carried out with or without a solvent solvents commonly employed are chloroform, benzene, petroleum ether, acetyl chloride and phosphorus oxychloride. 

The third approach is useful when the spiropyran itself (or, more correctly, its intermediates) is easily available, the necessary substituted intermediates are not, and the spiropyran tolerates the chemical transformations involved. Halogenation and nitration of BIPS and spiro(dinaphthopyrans) can be carried out by standard methods bromo substituents replaced by cyano or lithium, nitro substituents reduced to amino, etc. For example, the aldehyde group in 6-formylBIPS can be reduced, oxidized, caused to react with organometallics, condensed with active methylene groups, converted to cyano, and derivatized to give a wide variety of 6-substituted BIPS. These reactions cannot be usefully carried out directly on 5-formylsalicylal-... 

Protocol 3 is an example of an aza-Wittig reaction using l,2-bis(diphenyl-phosphino)ethane (DPPE or DIPHOS). The IMP is generated by reduction of the azide by DPPE, intramolecular reaction with the aldehyde group then occurs. It is worth noting the replacement of triphenylphosphine with DPPE. In the reaction... 

Historically, the first replacement of a diazonium group by hydrogen was accomplished with alcohols.Of these, ethanol is the best, while methanol tends to convert diazonium compounds to aryl methyl ethers. " The hydrogen atom replacing the diazonium group comes from the alcohol, which is converted to the corresponding aldehyde. The reaction is catalyzed by UV irradiation " and by copper(I) oxide. "" " Copper(I) oxide alone reduces the diazonium compounds, but in poor yields. " The reaction can be carried out in aqueous media " or in organic solvents. ""- " ... 

With furfural, the oxygen of the aldehyde group, as well as that of the furan ring, was replaced by sulfur. In addition, condensation and cleavage reactions led to a complex mixture of products. 

Preparative importance attaches to the crossed Cannizzaro reaction of formaldehyde with aldehydes that contain hydrogen on the -carbon atom. These hydrogen atoms are replaced by hydroxymethyl groups, and the aldehyde groups are reduced to alcohols by the excess of formaldehyde. Aldehydes containing two -hydrogen atoms give tris(hydroxymethyl)alkanes 504... 

The reactions of the phenolic aldehydes may be conveniently grouped under etherification of the phenolic hydroxyl group, replacement of the aldehyde group and condensation reaction of the latter. 

Syntheses of 4,5-Unsaturated Cyclic Compounds - Swem oxidation of methyl 2,3,4-tri-C>-acetyl-a-D-glucopyranoside followed by base-induced elimination of acetic acid afforded unsaturated aldehyde 33. Further transformation of the aldehyde group into a methylene unit by way of a Wittig olefination and replacement of the acyl groups with benzyls or methyls yielded 34 which underwent a Diels-Alder reaction (the acyl protected variant of 34 was unreac-tive) with 2-methoxycarbonyl-p-benzoquinone, followed by acid-catalysed double... 

As mentioned in Section 1.1, imines are also excellent electrophiles and could replace aldehydes to participate in an MBH reaction, the so-called aza-MBH reaction. The first example of imines involved in the aza-MBH reaction date back to 1984. Perlmutter and Teo reported that A-tosyl imines reacted with ethyl acrylate in the presence of DABCO as catalyst in a sealed tube to give adducts in moderate to good yields (Scheme 1.71). Since then, many kind of imines (174-182, Figure 1.5) bearing different activating groups have been developed and... 

Mitsui Toatsu investigated the rhodium-catalyzed version of this reaction, which can be conducted at a much lower syngas pressure (Scheme 4.22) [10]. To avoid deterioration of the catalyst by HCl, a buffer or an amine was added. 2-Chloropropionaldehyde, which is preferentially obtained, might be converted into racemic lactic acid by oxidation of the aldehyde group and replacement of the chloro substituent by a hydroxy group in a basic medium [11]. Alternatively, treatment of 2-chloropropionic acid with aqueous ammonia produces racemic alanine. 

---