Cyclohexane-1,2-diacetal protection group

Only short comments will be given for other acetal dnivatives fiiat are less pq ular. Chart 1 presents a list of formulae of cyclic acetals, mainly, those wifii five- and six-member rings (1,3-dioxolanes and 1,3-dioxanes). Seven-membered ring acetals are omitted because they are scarcely represented in carbohydrate chmnistry. The special case of spiroacetals and cyclohexane-l,2-diacetal-protecting groups, which have been reported recently, will be presented in Part n. 

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... 

Further research within in our laboratory has illustrated that certain substrates bearing trans-hydroxyl groups can be directly protected using cyclic and acyclic diones, thus alleviating the requirement for prior formation of the tetramethoxydiacetals.6 For example, butane-2,3-dione has proved particularly useful for the preparation of butane diacetal (BDA) derivatives, which serve as useful alternatives to cyclohexane diacetal (CDA) derivatives. 

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. 

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... 

There are some other remote protecting groups which are not the usual electron-withdrawing groups, but they still deactivate glycosyl donors 4,6-benzyUdene acetal, 3,4-cyclohexylidene diacetal (cyclohexane-1,2-diacetal CD A), dispiroketal (dispoke), and butane diacetal (BDA) (Fig. 2). 

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. 

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. 

Cyclohexane-1,2-diacetal (CDA) and dispiroketal (dispoke) protocols provide bulkier groups for rran -I,2-diol protection [86]. 

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