Diacetal protecting group

Only short comments will be given for other acetal derivatives that are less popular Chart 1 presents a list of formulae of cyclic acetals, mainly, those with five- and six-membered rings (1,3-dioxolanes and 1,3-dioxanes). Seven-membered ring acetals are omitted because they are scarcely represented in carbohydrate chemistry. The special case of spiroacetah and cydohexane-l,2-diacetal-protecting groups, which have been reported recently, will be presented in Part K. 

Diacetal Protecting Groups The pioneer work of Ley s group concerning the application of 1,2-diacetals such as the dispiroketal (dispoke) [141,142,143,144,145], the cyclo-hexane-... 

Notes and discussion. This procedure shows another versatile method for the interconversion of anomeric functionality. The glycosyl fluoride formed in this case bears a butane-1,2-diacetal protecting group, which is introduced under acidic conditions. The fluoride may be unstable to these conditions, whereas protection of a thioglycoside is possible. The synthetic strategy therefore effectively involves the use of a thioglycoside as a masked glycosyl fluoride. The procedure described... 

The stability of these 1,2-diacetal protected monosaccharides to standard reactions, such as silylation, benzylatiOTi or benzoylation, was investigated. Cleavage of the 1,2-diacetal protective groups is readily achieved under acidic conditions (aqueous trifluoroacetic) that do not tamper with glycosidic linkages (Scheme 5) [36]. 

With the aim of calculating the DF for the 1,2-diacetal protecting groups, a set of competition experiments related to those shown in Scheme 6 was performed [54, 55]. 

Reduction with sodium borohydride without protecting groups, 92 Reductive deacetoxylation of ll-keto-12/3-hydroxytigogenin diacetate, 53 Reductive methylation of the 3-ethylene ketal of pregna-5, 16-diene-3, 20-dione, 54... 

Until recently, the protection of the trans-hydroxyl groups of sugars has been an inefficient process.2 This protection has now been simplified by the introduction of the dispiroketal protecting group,3 and the cyclohexane diacetal (CDA) protecting group.4... 

Removal of the silyl protecting group using TBAF, and subsequent acetylation, led to the diacetate 818. Regioselective nitration and catalytic hydrogenation provided the (R)-arylamine 814 (613) (Scheme 5.95). 

Acylals (geminal diacetates) are frequently used as protecting groups for aldehydes because of their stability to neutral and basic conditions [8]. In addition, the acylal functionality can be converted into other useful functional groups [9]. For example a novel synthesis of chiral allylic esters has been developed using palladium-catalyzed asymmetric allylic alkylation of gem-diesters [10]. The allylation of... 

A wide variety of sulfonyl or carboxyl amides can be applied as nitrogen sources and nontoxic iodobenzene diacetate serves as a mild oxidant. Furthermore, the reaction conditions (e.g., room temperature) are mild, and the imina-tion proceeds with retention of configuration at the stereogenic sulfur (as shown in Scheme 2.1.1.3 for the conversion of (R)-14 into (i )-15). Most importantly, sulfoximine derivatives with easy-to-cleave protective groups at the sulfoximine nitrogen are obtainable, which allow access to the synthetically important free NH-sulfoximines (vide infra). 

Benzylidene and isopropylidene acetals of irons-1,2-diols are very labile as a result of ring strain and are not often used for synthetic applications. Fortunately, the protection of these diols can be accomplished with the recently developed dispiroketal (dispoke)35 and cyclohexane-1,2-diacetal (CDA) groups.36... 

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