Protection Of aldehyde

See Section 362 (Ester-Alkene) for the formation of enol esters and Section 367 (Ether-Alkenes) for the formation of enol ethers. Many of the methods in Section 60A (Protection of Aldehydes) are also applicable to ketones. 

See Section 60A (Protection of Aldehydes) and Section 180A (Protection of Ketones) for reactions involving formation of Acetals and Ketals. 

As a consequence, thiols are preferred to alcohols for the protection of aldehyde and ketone groups in synthetic procedures. Thioacetals and thioketals are... 

Dioxanes, like other acetals and ketals, are labile to dilute acid and this property has been exploited in schemes for the protection of aldehydes and ketones as well as for... 

Protection of aldehydes and ketones.1 The reagent reacts with aldehydes or ketones in refluxing ethanol (4-24 hours) to form 3-methylbenzothiazolines (2) in —70-90% yield. Aldehydes usually react so much more readily than ketones that selective protection is possible. Deprotection is effected in 90-98% yield by treatment with AgN03 in aqueous CH3CN at pH 7 or by reaction with HgCl2 in refluxing aqueous CH3CN. 

Protection of aldehydes and ketones.1 Bis-o-nitrobenzyl acetals or ketals are removable in 85-95% yield on irradiation at 350 nm in benzene. The acetals or ketals are easily prepared from 1 by an exchange reaction using 2,2-dimethoxy-propane (1, 268-269) catalyzed by an arenesulfonic acid. In the case of hindered ketones (17-keto steroids), the glycol o-N02C6H4CH(OH)CH2OH (2) can be used. 

Acetalization (see Addition reactions to carbonyl groups, Protection of aldehydes and ketones)... 

HBF4-silica also exhibits high activity in the protection of aldehydes as 1,1-diacetates (acylals)671 [Eq. (5.237), Table 5.38]. Both aliphatic and aromatic aldehydes react readily to form diacetates in high yields. The catalyst can be reused with marginal decrease in activity. 

In addition to developing a facile route to the synthesis of thioacetals and thioketals, optimization of the reagents residence time within the packed bed enabled the authors to demonstrate the chemoselective protection of aldehydic functionalities in the presence of ketonic moieties (Scheme 34). 

This Chapter contains reactions which prepare the oxides of nitrogen, sulfur, and selenium. Included are N-oxides, nitroso, nitro compounds, nitrile oxides, sulfoxides, selenoxides, and sulfones. Oximes are found in Sections 60A (Protection of Aldehydes) and 180A (Protection of Ketones). Preparation of sulfonic acid derivatives are found in Chapter Two and the preparation of sulfonates in Chapter Ten. 

Selective protection of aldehydes vs. ketones, 218 of amino vs. carboxyl groups, 270 of a- vs. co-amino and carboxyl groups in amino acids, 373... 

Ti(ISRi)i (1), Ti(NR,)4, R = CH, or C,H, is an excellent reagent for in situ protection of aldehydes and ketones by formation of adducts that revert to the original carbonyl compounds on aqueous work-up. Both la. R = CH, and lb, R = C,H, react more readily with aldehydes than with ketones, but la is more reactive in general than lb. Thus selective reactions can be conducted on a ketone group in the presence of an aldehyde group (equation I). The method can also be used to carry out selective reaction... 

Protection of aldehydes and ketones. Treatment of a dimethyl or diethyl acetal with 1.5 eq. of trichloroethanoi in refluxing benzene under acid cataly.sis (p-TsOH) gives the mixed acetal use of 4 eq. of the alcohol gives the di-2,2,2-trichloroethyl acetal. 

Various carbonyl compounds were efficiently converted into the corresponding 1,3-dithiolanes using triethyl orthoformate as a water scavenger and (bromodimethyl)sulfonium bromide as an efficient catalyst under solvent-free conditions <2004EJ02002>. This protocol can be applied for the chemoselective protection of aldehydes in the presence of ketones on a large scale (Equation 73). 

The diacetyl-substituted 2-vinylidene 1,3-dithiolane 645 was a much more effective transdithioacetalization reagent than 643 and gave the 1,3-dithiolanes 644 in 70-99% yields (Equation 88). Moreover, 645 was not only a nonthiolic, odorless 1,2-dithiol equivalent but also exhibited high chemoselectivity for protection of aldehyde in the presence of ketone <2004SL999>. 

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