Protecting group for aldehydes and ketones

Acetals are useful because they can act as protecting groups for aldehydes and ketones in the same way that trimethylsilyl ethers act as protecting groups for alcohols (Section 17.8). As we saw previously, it sometimes happens that one functional group interferes with intended chemistry elsewhere... 

While C-C bond formation via metallation and alkyl or aryl halides is well known (COMC (1982) 5.4.2.7.5), the C-C bond formation with TBAF and aldehyde, enones, or enals is new (Figure 9).318 Carboranyl groups can actually be used as protecting groups for aldehydes and ketones due to the facile cleavage of the cage C-C(OH) bond with... 

Cyclic acetals are useful and common protecting groups for aldehydes and ketones, especially during the course of a total synthesis [8]. The successful synthesis of acetals frequently relies on the removal of water, a by-product of the reaction between the carbonyl compound and the corresponding diol. A Dean-Stark trap is often used for the removal of water as an azeotrope with benzene, but this method is not suitable for small-scale reactions. In addition, the highly carcinogenic nature of benzene makes it an undesirable solvent. Many of the reported catalysts for acetal synthesis such as p-toluenesulfonic acid and boron trifluoride etherate are toxic and corrosive. 

Acyclic acetals are simple protecting groups for aldehydes and ketones, and we have previously reported their synthesis catalyzed by Bi(OTf)3 [104]. Acyclic acetals can also be converted to other useful functional groups. For example, allylation of acyclic acetals to give homoallyl ethers has been well investigated, and we have reported a Bi(OTf)3-catalyzed method for the same [105]. The success of Bi(OTf)3-catalyzed formation and allylation of acyclic acetals prompted us to develop a one-pot method for the synthesis of homoallyl ethers from aldehydes, catalyzed by bismuth triflate. A one-pot process saves steps by eliminating the need for isolation of the intermediate and thus minimizes waste. Three one-pot procedures for the synthesis of homoallyl ethers were developed [106]. 

Gravel, D., Hebert, J. and Thoraval, D. (1983) o-Nitrophenylethylene glycol as photoremovable protective group for aldehydes and ketones syntheses, scope, and limitations. Canadian Journal of Chemistry, 61, 400—410. 

Our final example is a base-labile 4-(phenylsulfonyl)methyl-l,3-dioxolane protecting group for aldehydes and ketones.4 Protection is carried out by the reaction of diol 17,1 (obtained by dihydroxylation of ally phenyl sulfone) with a carbonyl compound in the presence of pyridinium p-toluene sulfonate [Scheme 2.17], Cleavage is accomplished by treatment with DBU. /erf-Butyldimethylsilyl ethers, p-toluenesulfonate esters, tetrahydropyranyl ethers, carboxylic esters and benzoates are well tolerated. A disadvantage to the use of 17.1 is the introduc-... 

Acetal (Section 21.14) A compound having the general structure R2C(0R )2, where R = H, alkyl, or aryl. Acetals are used as protecting groups for aldehydes and ketones. 

In this section, the protections and cleavages of four protecting groups for aldehydes and ketones are presented dimethylketal 1,3-dioxane 1,3-dioxolanc and 1,3-dithiane. 

The practical use of 1,3-dithioles as synthons in organic synthesis is small whereas 1,3-dithiolanes are quite often used as protecting groups for aldehydes and ketones <92HOU(El4a/3)403). TTF and... 

Acetals are extremely useful compounds in synthesis because they can act as protecting groups for aldehydes and ketones. 

Vert de lilas is useful as an additive in soaps since acetals, unlike aldehydes and ketones, are stable to the alkali in soaps. The main use tor acetals in synthesis is as protecting groups for aldehydes and ketones (see Chapter 9). Cyclic acetals (e.g, 4) are usually used for ketones (Chapter 7) the disconnection is the same once the carbonyl carbon has been discovered. 

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