Unsaturated aldehydes halogenation

While there are no examples of the formation of fluorinated unsaturated aldehydes by de-halogenation, dehalogenation is the preferred method for the synthesis of reactive fluorinated ketenes. Examples of dehalogenations giving unsaturated fluorinated ketones and fluorinated ketenes are listed in Table 9. 

Electrophilic addition of hydrogen halides to a,/f-unsaturated aldehydes and ketones places the halogen on the /3 carbon. This orientation is opposite to that observed for related additions to conjugated dienes ... 

Iridium,204,205 together with osmium, has been not widely used in catalytic hydrogenation. Recently, however, iridium or iridium-based catalysts have been shown to be effective in various hydrogenations, such as in selective hydrogenation of a,P-unsaturated aldehydes to allylic alcohols (Section 5.2), of aromatic nitro compounds to the corresponding hydroxylamines (Section 9.3.6), of halonitrobenzenes to haloanilines without loss of halogen (Section 9.3.2), and in the stereoselective hydrogenation of carbon to carbon double bonds (see, e.g., eqs. 3.25-3.27 and Table... 

The halogen appears at the / -position when HX is added to, / -unsaturated aldehydes, ketones, acids, or nitriles whether the addition is electrophilic with addition of H+ as primary step or nucleophilic with addition of X as primary step. The reaction is preparatively important for synthesis of / -halo acids, esters, and nitriles. 

Organic compounds, such as alcohols aldehydes halogenated-, nitrated-, and unsaturated... 

Vilsmeier reaction to the chloroaldehyde (106), followed by reductive meth-ylation, yielded the aldehyde 107 (Scheme 14) with the precedented stereochemical outcome. Attempted halogenation of the derived neopentyl-type alcohol was unsuccessful under a variety of conditions, so an alternative scheme involving two successive Wittig-type reactions was developed. The aldehyde 107 was converted to the unsaturated aldehyde 108 by the method of Nagata and Hayase. Reduction with triethylsilane and tris (triphenylphosphine) rhodium chloride was followed by condensation with isopropylidene phosphorane to give the desired product 109. 

Organocatalytic asymmetric carbon-halogen bond-forming reactions have been combined with other catalytic asymmetric reactions in a single flask to effect cascade reactions. Quintard and Alexakis [78] developed a cascade reaction in which a Cu-catalyzed conjugate addition to an a,p-unsaturated aldehyde was followed by an enamine-catalyzed a-fluorination or chlorination. 

Arsenic, Antimony, and Bismuth.- (Diphenylarsino)methyl-lithium (203) has been prepared by either halogen-lithium or tin-lithium exchange from (204) or (205) respectively. Interestingly the reactivity of (203) depends on the method of preparation used, although the reasons for this are not known. A stereoselective synthesis of JE-a, -unsaturated aldehydes has been achieved by reacting aldehydes with the arsonium salt (206) in the presence of a weak base. The ylide derived from (206) shows a reasonable... 

A one-step Lewis acid-catalysed intermolecular 4- -3-cycloaddition of aromatic a,)3-unsaturated aldehyde and ketones (105) with epoxides (106) formed seven-membered oxacycles (107) under mild conditions (Scheme 34).The effect of oxygen-, sulfur-, and halogen-substituents on the reactivity of nitrogen-stabilized oxyallyl cations in 4- -3-cycloaddition reactions has been extensively investigated. Aza-oxyallyl cationic intermediates react with cyclopentadiene and furan via an aza-4 -I- 3-cycloaddition reaction to form bicyclic cycloadducts in moderate yields. The intramolecular formal 4- -4-cycloaddition of conjugated enynes with an e-deflcient cyclobutene (108) yielded a strained six-membered cyclic allene (109) that isomerized to a 1,3-cyclohexadiene (110). This intermediate underwent a thermal or acid-promoted six-electron electrocyclic ring opening to yield a 2,4,6-cyclooctatrienone (111) (Scheme 35). ... 

Oioxolanes derived froma holoaldehydes, when treated with KF in ethylene glycol/ undergo dehydrohalogenation without halogen interchange. This is a useful route to a great variety of a, p-unsaturated aldehydes. ... 

Historically the first cascade Michael-alkylation reaction was described almost simultaneously by the Wang and the Cordova groups by using a,(i-unsaturated aldehydes with bromomalonates or bromoacetoacetates. The reaction afforded cyclopropanes or cyclopentenones depending on the position of the halogen and was catalyzed by diphenylproHnol TMS ether (6) (Scheme 25.2) [5a,b]. 

In this chapter we examine the thermal reactions of the several classes of the aldehydes in the atmosphere aldehydes with saturated hydrocarbon chains (alkanals), hydroxyaldehydes, dialdehydes (with saturated and unsaturated hydrocarbon chains), unsaturated aldehydes, aldehydes derived from aromatic and biogenic hydrocarbons and halogen substituted aldehydes. The rate coefficients and mechanisms of atmospheric oxidation of the alkanals are reviewed in the following section (IV-B), which draws on the analysis provided by Calvert et al. (2008) for reactions of alkanals with OH and NO3 with an update of information where it is available. 

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