Cyclohexane-1,2-diacetals

The rigid CDA group depresses the reactivity of the glycosidic centre owing to the increase in strain consequent to flattening the pyranose ring as it forms an oxonium ion intermediate. This torsional deactivation has important conse- 

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Oxacyclopentylidene, 234 Butane-2,3-bisacetal, 235 Cyclohexane-1,2-diacetal, 235 Dispiroketals, 236... 

Two new methods have been discovered for the selective protection of mmr-diequatorial vicinal diols [44,45]. One of them uses 3,3, 4,4 -tettahydro-6,6 -bi-2W-pyran (bis-DHP) 40 to transform diols into dispiroacetals and the second uses 1,1,2,2-tetrahydromethoxycyclo-hexane 41 to obtain cyclohexane-1,2-diacetal-protected sugars. These two methods have been compared [44,45] and we give here, as representative examples, one procedure for each strategy. 

Benzylidene and isopropylidene acetals are often used for the selective protection 1,2-cis or 1,3-cisjtrans diols of sugar derivatives. They are stable to strong basic conditions but quite fragile towards acid. Recently, dispirodiketal and cyclohexane-1,2-diacetal groups have been introduced to protect selectively 1,2-trans diols of carbohydrates. 

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... 

Ley SV, Priepke HWM, Warriner SL. Cyclohexane-1,2-diacetals in synthesis 1. Cyclohexane-1,2-diacetals (CDA)—A new protecting group for vicinal diols in carbohydrates. Angew. Chem. Int. Ed. 1994 33 2290-2292. 

A facile one-pot synthesis of a trisaccharide unit from the 51. common polysaccharide antigen of group B Streptococci using cyclohexane-1,2-diacetal (CDA) protected rhamnosides. Angew. 

Grice, P, Ley, S V, Pietruszka, J, Osborn, H M I, Priepke, H W M, Warriner, S L, A new strategy for oligosaccharide assembly exploiting cyclohexane-1,2-diacetal methodology an efficient synthesis of a high mannose type nonasaccharide, Chem. Eur. J.,3, 431-440, 1997. 

Isopropylidene (acetonides) and benzylidene derivatives are the most commonly used acetals for the simultaneous protection of 1,2- and 1,3-diols in carbohydrate and nucleoside chemistry [123]. Cyclohexylidene acetals are occasionally used, most often as an alternative to benzylidene acetals. Protection using cyclohexane- 1,2-diacetals or the related butane-2,3-diacetals represents a new approach which has proved its value in complex oligosaccharide synthesis [124]. 

Dimethoxyethylidene, 349 a-Methoxybenzylidene, 349 l-(A,A-Dimethylamino)ethylidene Derivative, 349 (X-(A,A-Dimethylamino) benzylidene Derivative, 349 Butane-2,3-bisacetal, 350 Cyclohexane-1,2-diacetal, 351 Dispiroketals, 352... 

Douglas et al. [19]. discovered that the cyclohexane-1,2-diacetal (CDA) protection group (e.g., 48) (Fig. 5.13) as weU as the octahydro-2,2 -bi-2H-pyran-2,2 -diyl (dispoke) group (e.g., 47) had a reactivity tuning effect between that of the fully... 

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