Butane-2.3-diacetals

Extensive NMR data has been recorded and assigned for various l,2-diacetdls in the monosaccharide series by the Ley group. -  

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To address limitations in the use of glyceraldehyde acetonide (43) as a three-carbon chiral building block, butane-2,3-diacetal-protected glyceraldehyde (44, R1 = R2 = H) has been prepared. It undergoes diastereoselective aldol reactions with a range of carbonyl compounds esters, thioesters, and ketones. The work has been extended (g) to other derivatives such as the a-substituted aldehyde (44, R1 = Me, allyl) and the methyl ketone (44, R2 = Me).122a,b... 

The simultaneous and selective protection of the two equatorial hydroxyl groups in methyl dihydroquinate [11L1, Scheme 3.111 j as the butane-2,3-diace-tal 111 2 was a key strategic feature in a synthesis of inhibitors of 3-dehydroqui-nate synthase.205 Later in the synthesis, deprotection of intermediate 111.4 required three steps (a) hydrolysis of the trimethylsilyl ether and the butane-2,3-diacetal with trifluoroacetic acid (b) cleavage of the isopropyl phosphonate with bromotrimethylsilane and (c) hydrolysis of the methyl ester with aqueous sodium hydroxide. Compound 111 1 has also been used in the synthesis of inhibitors 3-dehydroquinate dehydratase206 and influenza neuraminadase207-208 as well as shikimic add derivatives.209 210... 

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]. 

Likewise, butane-2,3-diacetals (BDA) are good protecting groups for vicinal diequatorial diols. They are prepared either from butane-2,3-dione [153] or from the tetramethoxy butane-2,3-diacetal [147] (O Scheme 23). BDA derivatives are usually isolated as solids rather than... 

Dispoke Derivatives 161 Cyck)hexane-1 -diacetals Butane-2,3-diacetals 165... 

Later, it was shown that 2,2,3,3-tetramethoxybutane (TMB) 7 [33] is also an efficient selective protecting group for diequatorial 1,2-diols, providing butane-2,3 diacetals (BDA) in good to excellent yields (Scheme 4a). Soon after, TMC 2 and TMB 7 were replaced by their corresponding synthetic precursors cyclohexene-1,2-dione 8 and butane-2,3-dione 9 [34, 35]. 

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