Formyl groups, metalation

The formyl group provides enough activation so that lithium fluoride will convert 5-bromofuran-2-carboxaldehyde into 5-fluorofuran-2-carboxalde-hyde, but only in dimethylformamide at 100°C. Other metal cations are ineffective. Replacement by other halogens is easy, the chloride-bromide displacement being reversible.180... 

To summarize briefly, our approach involves initial attack by a relatively nucleophilic metal hydride on coordinated CO. Such reactivity has been demonstrated repeatedly for main-group metal hydrides perhaps the most elegantly worked-out system involves CpRe(C0)2(N0)+ (Cp = Tl-C H ) which, under varying conditions, can be converted to an entire range of products containing CO at different stages of reduction, including formyl, carbene, hydroxymethyl and methyl species (Scheme l). Reactions lead-... 

Formic esters homologation - Ruthenium catalysts based on [Ru(00)3X3] species are sole Group VXIX metal systems able to hydrogenate and homologate the formyl group of formic esters to methyl and acetyl derivatives without causing an extensive decarbonylation of the formyl moiety (eqs.7,8) (17). 

A formyl group can be introduced by reacting the metallated acetylene (M = Li or MgX) with a NjN-disubstituted fonnamide or with a formic ester [84-86] ... 

All the reactions described above rely on the electrophilic reactivity of the carbonyl C atom of the aldehyde 2. Much effort was devoted to the development of phosphaferrocenes with nucleophilic reactivity at this position. For example, transformation of the formyl group into a halomethyl function would pave the way for the preparation of Grignard or lithium derivatives by halogen-metal exchange. However, all attempts to do this were unsuccessful. 

Repulsive electrostatic interactions seem to determine (82CPB3442) the conformation of the formyl group in 1,2,3,6-tetrahydropyridines 72 the conformation represented is of higher energy, but is favored in the presence of metal chelating agents. 

It was discovered by Roelen in 1938 and is the oldest and largest volume catalytic reaction of alkenes, with the conversion of propylene to butyraldehyde being the mosi important. About 5 million tons of aldehydes and aldehyde derivatives (mostly alcohols) are produced annually making the process the most important industrial synthesis using a metal carbonyl complex as a catalyst. The name hydroformylation arises from the fact that in a formal sense a hydrogen atom and. formyl group are added across a double bond. The net result of the process is extension of (he carbon chain by one and introduction of oxygen into the molecule. 

As well as the above addition and elimination sequences, metal-catalyzed nucleophilic addition can occur. Examples include the zinc(II)-catalyzed hydride ion addition in the reduction of the formyl group of the phenanthroline aldehyde (49)91 and the copper(II)-catalyzed ring opening of 2-pyridyloxirane (50)92 (equations 22 and 23). 

The use of a formyl group as a directing functionality is challenging because, in the case of the low-valent transition metal-catalyzed reaction of aldehydes with an olefin, aldehydes are prone to undergo decarbonylation or hydroacylation of the olefins. The following protocol to suppress the decarbonylation, one being steric and the other electronic in nature, can be used. In the case of the reaction of 1-methylin-dole-3-carboxaldehyde with ethylene, the ethylation product is also obtained in quantitative yield (Eq. 9.5) [13]. 

The formylation of metalated sp carbons, for example in a stannylbenzene (Eq. 185) [458] or in vinylsilanes [459,460] (Eq. 186), with Cl2CH(OMe) and TiCU, in which the ipso carbon to the stannyl or silyl group is selectively formylated, has been reported. The formylation of a vinylsilane was used in the preparation of a terpene aldehyde, nuciferal, as shown in Eq. (186) [461]. 

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