Aldehydes, addition derivatives chlorination

Dipolar addition of ethyl propiolate to the nitrile oxide 285, prepared by chlorination of the corresponding oxime, gave, after removal of protecting groups, the C-glycosyl-isoxazole205 (286). These reactions further demonstrate the utility of anomerically functionalized C-/3-D-ribofuranosyl derivatives that can be prepared from the versatile aldehyde 100. 

The methoxide ion uses of its lone pairs of electrons to form a bond to the electrophilic carbonyl carbon of the acid chloride. Simultaneously, the relatively weak n bond of the carbonyl group breaks and both of the n electrons move onto the carbonyl oxygen to give it a third lone pair of electrons and a negative charge. This is exactly the same first step involved in nucleophilic addition to aldehydes and ketones. However, with an aldehyde or a ketone, the tetrahedral structure is the final product. With carboxylic acid derivatives, the lone pair of electrons on oxygen return to reform the carbonyl n bond (Step 2). As this happens, the C-Cl o bond breaks with both electrons moving onto the chlorine to form a chloride ion that departs the molecule. 

Tomboulian et al. (2002) has reported that butylated hydroxytoluene (BHT) can impart a "burnt plastic" odor and is an additive in HDPE pipes. Quinone may be derived from BHT due to interactions with residual chlorine in pipes (Anselme et al., 1985). Yam et al. (1996) reported that antioxidants, such as vitamin E, Irganox 1010, and BHT, contributed to off-flavors in water. Vitamin E yielded less off-flavor, possibly due to lower aldehyde and ketone concentrations. Extrusion temperatures over 280 °C and exposure time for melt contributed to more oxidation of LDPE films and higher intensities of off-flavors in water in contact with LDPE with different antioxidants (Andersson et al., 2005). 

Dimethyl sulfoxide and chlorine form highly reactive intermediates which are of some limited use as oxidants for alcohols. These intermediates are related to those derived from the reaction of the halogens with dimethyl sulfide and probably have a structure such as (27). When formed at -4S C they allow the oxidation of primary and secondary alcdiols to aldehydes and ketones when used in a two-fold excess. For very simple alcdiols the reaction proceeds in yields of greater than 90%, but there are considerable drawbacks if some types of additional functionality are present in the molecule, e.g. alkenes react very rapidly to form vicinal dichlorides. 

Benzylidene chloride and its nuclear-substituted derivatives are important mainly as intermediates on the way to aldehydes, so that the difficulty of separating them from benzotri-chlorides must be overcome. On hydrolysis they give benzoic acids, which are readily separable from the aldehydes. Phosphorus trichloride (ca. 2%) has been recommended as addition for side-chain chlorination of toluenes. 

The addition of phosgene to aldehydes 1757, as catalyzed by naked chloride anions, opened a synthetic route to a-chlorinated chloroformates 1758 and their derivatives, which are useful as pharmaceutical intermediates [49, 1290-1292]. 

The MacMillan group developed an impressive array and complexity of highly enantioselective SOMO transformations with the addition of enamine-derived radical cations to electron-rich olefins, allowing the aUylation, enolation, vinylation, styrenation, chlorination, polyene cydization, arylation, benzylation, and alkylation of a range of aldehydes (Scheme 39.3) [le, 5a, 5b, 6,8c, 13]. A common mechanistic... 

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