Halide To aldehyde

The conversion of alkyl halides to aldehydes is a synthetic step... 

In all the desulphonylation reactions discussed in Sections III.B and III.C the sulphur is lost from the starting sulphone and is reduced in the process simultaneously, the former carbon-sulphur bond is either reduced to a C—H bond or is converted into a C=C bond. The reactions described in this section have the common thread that the sulphur atom is lost with reduction at sulphur, but the carbon atom is converted directly into a carbonyl group. Formally, these reactions offer a route from alkyl halides to aldehydes or ketones. 

Another reagent that convert benzylic halides to aldehydes is pyridine followed by /7-nitrosodimethylaniline and then water, called the Krohnke reaction. Primary halides and tosylates have been oxidized to aldehydes by trimethylamine N-oxide, and by pyridine N-oxide with microwave irradiation. ... 

The direct addition of simple alkyl groups onto aldehydes is the most challenging in water. Mitzel reported the indium-mediated alkylation of carbonyl compounds with a-sulfur stabilized systems.224 Recently, Li and co-workers reported an efficient addition of simple alkyl halides to aldehydes mediated by Zn/Cul with a catalytic amount of InCl in water (Eq. 8.89).225... 

The multi-component procedure is also effective for the chromium-catalyzed addition of organic halides to aldehydes (the Nozaki-Hiyama-Kishi reaction) [73]. The active Cr(II) species is recycled by redox interaction with Mn powder as the stoichiometric co-reductant in the presence of MesSiCl (Scheme 34), which mainly liberates the chromium catalyst from the alkoxide adduct. The chemo- and diastereo-selective addition reaction is performed with a variety of organic halides and alkenyl triflates. In the case of crotyl bromide, the addition is highly stereoconvergent, i.e., the respective anti-... 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

The development of the Grignard-type addition to carbonyl compounds mediated by transition metals would be of interest as the compatibility with a variety of functionality would be expected under the reaction conditions employed. One example has been reported on the addition of allyl halides to aldehydes in the presence of cobalt or nickel metal however, yields were low (up to 22%). Benzylic nickel halides prepared in situ by the oxidative addition of benzyl halides to metallic nickel were found to add to benzil and give the corresponding 3-hydroxyketones in high yields(46). The reaction appears to be quite general and will tolerate a wide range of functionality. 

Homoallylic alcohols (8, 111-112). CrCl2, prepared in situ by reduction of CrCl, (Strem) in THF with Na/Hg, is superior to CrCl2 prepared by reduction of CrCl, with LiAlHj for the Cr(II)-mediated addition of crotyl halides to aldehydes. The homoallylic alcohols are formed in good yield and with high arm-selectivity.7 Example ... 

Cr-Ni bimetallic catalyst-promoted redox addition of vinyl halides to aldehydes. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

The high diastereoselectivity observed is remarkable, particularly in view of the fact that addition of substituted allylzinc halides to aldehydes usually occurs without diastereoselectivity31. The high level of stereoselectivity in the allylation reaction was rationalized by a Zimmermann-Traxler chair-like transition state30. 

Direct Conversion of Alkyl Halides to Aldehydes and Ketones Formyl-de-halogenation... 

Another way to oxidize primary alkyl halides to aldehydes is by the use of hexamethylenetetramine followed by water. However, this reaction, called the Sommelet reaction. is limited to benzylic halides. The reaction is seldom useful when the R in RCH2CI is alkyl. The first part of the reaction is conversion to the amine ArCH2NH2 (0-44), which can be isolated. Reaction of the amine with excess hexamethylenetetramine gives the aldehyde. It is this last step that is the actual Sommelet reaction, though the entire process can be conducted without isolation of intermediates. Once the amine is formed, it is converted to an imine (ArCH2N=CH2) with formaldehyde liberated from the reagent. The key step then follows transfer of hydrogen from another mole of the arylamine to the imine ... 

The conversion of alkyl halides to aldehydes is a synthetic step of broad utility. Earlier procedures for such conversions involving the use of dimethyl sulfoxide7 or pyridine N-oxide 8... 

Table 49. In situ addition of allenyl/propargyl tin halides to aldehydes in water.

W. P. Neumann, Synthesis, 1987, 665 discusses the reduction of acyl halides to aldehydes with tri-n-butyltin hydride. 

The conversion of alkyl halides to aldehydes and ketones can also be accomplished indirectly (10-71). See also, 12-33. 

Oxidations with chromic oxide encompass hydroxylation of methylene [544] and methine [544, 545, 546] groups conversion of methyl groups into formyl groups [539, 547, 548, 549] or carboxylic groups [550, 55i] and of methylene groups into carbonyls [275, 552, 553, 554, 555] oxidation of aromatic hydrocarbons [556, 557, 555] and phenols [559] to quinones, of primary halides to aldehydes [540], and of secondary halides to ketones [560, 561] epoxidation of alkenes [562, 563,564, and oxidation of alkenes to ketones [565, 566] and to carboxylic acids [567, 565, 569]. 

Dimethyl sulfoxide (DMSO), (CH3)2SO, is a versatile reagent for the oxidation of alcohols to carbonyl compounds under gentle conditions. In addition to the previously mentioned dehydrogenations, it is capable of other oxidations acetylenes to a-diketones [997], alkyl halides to aldehydes 998, 999], tosyl esters to aldehydes [1000], methylene groups adjacent to carbonyl groups to carbonyls [1001, 1002], a-halocarbonyl compounds to u-dicarbonyl compounds [1003,1004,1005], aldehydes to acids [1006], and phosphine sulfides and selenides to phosphine oxides [1007]. 

A modification of the oxidation of alkyl halides to aldehydes is the transformation of the halides into alkyl tosylates on treatment with silver tosylate in acetonitrile at 0-5 °C followed by heating of the crude tosylates with dimethyl sulfoxide and sodium bicarbonate (equation 189) [1000],... 

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