Mannofuranose 2,3-0-isopropylidene

Fig. 3.—A. Initial Slope Approximation to Determine the Initial, Nonselective, Spin-Lattice Relaxation Rate of H-S of 2,3 S,6-Di-0-isopropylidene-a-D-mannofuranose (2) in Me2SO-d Solution. (Points between 0.01 and l.SS s were selected for tracing the best straight line.) B. The Same as in A for H-1 of a Partially Deuterated Sample of 1,6-Anhydro- -cellobiose Hexaacetate (3). [Note that the relaxation of H-1 is strongly dependent on the choice of I value. An R (ns) value of 0.24s was obtained from the data points 0 t 5s, where a value of 0.18 s was obtained from the terminal decay 5 lOs (see text).]...

For 2,3 5,6-di-O-isopropylidene-a-D-mannofuranose (183), separation of the anomeric products (184 and 185) was possible,135 and their structures were elucidated by periodate-oxidation studies. The configurational assignment for these products was based on the greater value of the specific rotation for the a anomer, as compared with that of the j3 anomer. The higher chromatographic mobility of one of the... 

Similarly, starting from 2,3 5,6-di-0-isopropylidene-D-mannofuranose 72, a one-pot procedure that implies the synthesis of glycosyl sulfones by Horner-Wadsworth-Emmons olefination with phosphonate 73, followed by subsequent Michael addition and Ramberg-Backlund reaction92 gives compound 74 in 78% yield93 (Scheme 24). 

Two reports on the preparation of polyhydroxylated [13]thiazolo[3,2a]azepane derivatives have been published. The one reports the synthesis of the p-tum mimetic 22 from D-glucurono-3,6-lactone and L-cysteine <99TL477>, whilst the other describes, for example the preparation of 23 in 78% yield from 6-0-tosyl-23-0 isopropylidene-D-mannofuranose and 2-aminothioethanol <99S839>. 

HaC-C-NOz 1 ch3 Na2S, DMF, bv ch3 2,3 5,6-Di-0-isopro- pyliden-l-desoxy-1- isopropyliden- mannofuranose 96 2... 

In a number of reactions on furanose derivatives, steric restraints interfere with anhydro-ring formation. 6-Deoxy-2,3-0-isopropylidene-5-O-tosyl-L-mannofuranose is readily converted by sodium methoxide into methyl 6-deoxy-2,3-0-isopropylidene-/3-D-allofuranoside. In this... 

The second example concerns the study of acetonation of o-mannose (see Scheme 8) and allows a clear distinction between the use of 2,2-dimethoxypropane and 2-methoxy-propene. Thus, whereas D-matmose gives 2,3 5,6-di-0-isopropylidene-D-mannofuranose 5 by reaction of the free sugar with acetone [5,6] as well as with 2,2-dimethoxypropane [96], the major compound (more than 85%) obtained with 2-methoxypropene is 4,6-0-isopropylidene-D-mannopyranose 6 [52]. Once again, a confirmation of the better stability of furanoid acetals in this series is given by the selective hydrolysis of the 2,3 4,6-di-O-isopropylidene-D-mannopyranose 7 (by-product of the preceding reaction or quantitatively obtained by action of 2-methoxypropene on acetal 6), witch gives the furanoid monoacetal 8. Actually, the pyranoid monoacetal 9 can be easily prepared as soon as the anomeric hydroxyl group is protected by acetylation [52]. 

Examples of sugar homologation based on the use of 2-lithio-l,3-dithiane (2-LDT, 13) are surprisingly rare relative to the popularity of this reagent [25]. Stereoselective chain extension of a partially protected hexose, 2,3 5,6-di-0-isopropylidene-ot-D-mannofuranose (14), into a D-glycem-D-galacto-heptose derivative (16) was reported by Paulsen and his coworkers several years ago [26] (Scheme 5). 

The fragmentation of l,2 5,6-di-0-isopropylidene-a-D-gIucofuranose (29) or 2,3 5,6-di-0-isopropylidene-D-mannofuranose starts with cleavage of the bond between C-4 and C-5. 

Variable-temperature 13C NMR spin-lattice relaxation time measurements have been used to probe the motional behavior of 2,3 5,6-di-O-isopropylidene-a-D-mannofuranose (22) in dimethyl sulfoxide solution.67 This carbohydrate deriva-... 

An asymmetric synthesis of aminocyclopentitols 134-137 has been used in the synthesis of trehazolin via free-radical cycloisomerization of enantiomerically pure, alkyne-tethered oxime ethers derived from D-mannose (Scheme 17).84 Treatment of 2,3 5,6-di-(9-isopropylidene-D-mannofuranose (128)85 with ethynylmagnesium bromide gave compound 129, which underwent sequential one-pot acid hydrolysis plus diol cleavage to give 130, oximation of which afforded the radical precursor 131, in 41% overall yield from 129. The free hydroxyl group of 131 was protected as acetate 132 and tert-butyldimethylsilyl ether 133, which were isolated as inseparable... 

The (+ )-isomers were prepared from 2,3-0-isopropylidene-D-ribofuranose (179) as shown Scheme 20. A very similar route from 2,3-0-isopropylidene-D-mannofuranose (180) led to the (-)-isomers. The naturally occurring isomers [( + )-173 and (-)-174] having the (2i )-configuration tasted more fruity, the configuration at C-4 having litde influence on Ae taste. 

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