Diol protection cyclohexane-1,2-diacetal

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

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. 

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]. 

Cyclohexane-l,2-diaceta] protection, a new protecting teduiique for vicinal diols, is illustrated in Scheme 5. It is selective for Crons-disposed hydroxyl grotqis giving mainly the 2,3-acetal of metl a-D-galactopyranoside, the 3,4-acetals of methyl a-D-maimo- and a-L-thamno- and a-D-lyxo-pyranoside, and 2,3/3,4-mixtures in the g/uco-seriesThe 3,4-0-( ohexane-l,2-diacetal) derivatives of methyl a-L-ihamnoside and ethyl l-thio-oi-L-rhamnoside were used successfully in a trisaccharide thesis (see Ch o 4), ... 

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