Carbon-chain homologations rearrangement

Reductive Junctionattzation of (aryhekninyl)acetatesJ When the Pummerer-type rearrangement of PhSe(0)CH2COOR is carried out in the presence of a reactive silane (e.g., allylsilanes, Me SiN,) carbon chain homologation or functionalization of the esters results. 

Water is not always split off in one direction only, and dehydration is often accompanied by isomerization, rearrangement, or even cleavage of the carbon chain. Thus heating 1-butanol with 85% phosphoric acid or 60% sulfuric acid leads to mixtures of 1- and 2-butene.1 In several cases the individual olefins can be isolated from the mixture of isomers by fractional distillation, as F. C. Whitmore and his colleagues found for the isomeric octenes.2 An isomerization that was actually desired occurs when cyclohexene or its homologs are heated over alumina at 470-480°, this affording alkylcyclopentenes.3... 

Homologation of a broad range of aliphatic acid structures and carbon numbers, with extensive rearrangement during the homologation of certain branched-chain acids. 

The base peak (mlz 59, H2NC(=OH+)CH2 ) in all straight-chain primary amides higher than propi-onamide results from the familiar McLafferty rearrangement. Branching at the a-carbon (CH3, etc.) gives a homologous peak at m/z 73 or 87,.... ... 

The carbon backbones of homologous proteins (especially closely related ones, such as orthologs) are often nearly superimposable in three-dimensional space.3 This type of observation led to the widespread belief that the observed differences in function between homologous enzymes are due primarily to replacements of amino acid side chains, rather than to rearrangements of the carbon backbone. For example, the backbones of the substrate binding pockets of cow CPA1 and CPB are nearly superimposable in three-dimensional space (not shown), suggesting that the differ-... 

One important application of this reaction is the chain extension of acyl chlorides to their homologous esters, known as the Amdt-Eistert reaction. Notice that the starting material for the Wolff rearrangement is easily made from RCO2H by reaction of the acyl chloride with diazomethane the product is RCH2CO2H—the carboxylic acid with one more carbon atom in the chain. A CH2 group, marked in black, comes from diazomethane and is inserted into the C-C bond between R and the carbonyl group. 

A straight chain diazomethyl ketone will also undergo Wolff rearrangement on irradiation. Such diazomethyl ketones are readily prepared from the corresponding acid chloride (150) by exposure to diazomethane or, more conveniently, trimethylsilyldiazomethane (Petrarch). Tlie net one-carbon homologation so effected is known as the Amdt-Eistert synthesis. 

If both the ester and the acid chains are of sufficient length (ethyl butanoate or larger), the hydrogen rearrangements of Equations 9.32 and 9.34 can occur consecutively these characteristic ions will appear at w/z 60 and 61 if the acid s a-carbon atom is not substituted. n-Heptyl and homologous higher carboxylates characteristically yield a low abundance ion corresponding to the butyl ester (Meyerson et al. 1983). 

---