Sugar allyltins

Intramolecular Diels-Alder reaction of chiral highly oxygenated trienoates derived from sugar allyltins [75]... 

An interesting approach to carbobicyclic polyhydroxylated compounds was proposed by Jarosz.43 It was based on a Lewis acid transformation of sugar allyltins 82 into dieno-aldehydes 83 with the fi-geometry across the internal double bond exclusively. The Wittig-type reaction of 83 afforded a triene, which underwent cyclization under high pressure, providing derivatives of bicyclo[4.3.0]nonane 84. Alternatively, dienoaldehyde 83 was converted into the phosphonate 85, which afforded the bicyclo[4.4.0]-decene derivatives (86) upon reaction with an aldehyde and simultaneous cyclization of the resulting triene.43 (Fig. 29). 

Sugar allyltins (mentioned already in 2.2.3.) were used for the preparation of higher carbon sugars. This may be illustrated by reaction of the furano-side 99 with di-O-isopropylidene-D-arabinose performed under high pressure, which provided compound 100 (Fig. 33).43,48... 

Sugar allyltin derivatives are very useful synthetic intermediates. The most convenient and reliable method for their preparation is a so-called xanthate procedure. The first compound of this class was prepared in 1988 by Mortlock and Thomas [74]. 1,2-0-isopropylidene-D-glycer-aldehyde (80) was converted into allylic alcohol and further transformed into the corresponding xanthate 81. This compound underwent thermal [3,3] rearrangement into the dithiocarbon-ate 81a, which upon reaction with tri-n-butyltin hydride provided the final sugar allyltin 82 as a mixture of isomers with the E-one strongly predominating (O Scheme 35). 

The controlled fragmentation of the primary sugar allyltins is a convenient method for the preparation of dienoaldehydes with the -configuration across the internal double bond. The Z-dienes are also available from sugar allyltins, but the secondary ones. When the sugar allylic mesylates (or chlorides) 86 reacted with a tin nucleophile, the Sn2 product 92 was obtained. 

Jarosz, S., and Skora, S., A convenient route to enantiomerically pure highly oxygenated decalins from sugar allyltin derivatives. Tetrahedron Asymmetry. 11, 1433, 2000. 

Reaction of aldohexofuranose 5,6-diols with TPP/imidazole/l2 has afforded the corresponding 5,6-unsaturated derivatives, while elimination of HBr from the 6-bromo compound 23, followed by hydroboration, has generated the product 24 with the L-ido configuration (Scheme 4). Some sugar allyltin derivatives (e.g. 

Sugar allyltin derivatives, convenient precursors of dienoaldehydes such as compounds 31, have been obtained by Sr2 reaction of trialkyltin radicals with allylic thiocarbonates which were, in turn, produced by Wittig condensation followed by a 3 3 thermal rearrangement, as shown in Scheme 5. ... 

Application of Sugar Allyltins in Stereocontrolled Organic Synthesis... 

The dienoaldehyde formed by decomposition (better to say controlled fragmentation) of the primary sugar allyltin (such as 59) had always the -geometry across the internal double bond, regardless of the configuration (E or Z) of the starting sugar... 

To prepare efficiently the opposite isomers, that is, cis-hydrindanes and trans-decalins, the access to the Z-dienoaldehyde was required. We have found that such Z-dienoaldehyde is available by thermal decomposition of the secondary sugar allyltin (72 in Figure 10.22). Its reaction with Ph3P=CHC02Me followed by cyclization... 

How does this reaction, that is, formation of the Z-dienoaldehyde, occur Treatment of the D-mamo-demed allylic mesylate 75 with the Lipshutz reagent ( Bu3SnCu ) afforded the secondary allyltin 76 as the predominant product [53] small amounts (< 1 %) of the epimer at the C-6 was also formed (Figure 10.23). We proved that thermal rearrangement of the secondary sugar allyltins proceeded via the concerted mechanism as shown in Figure 10.23 [41, 54]. 

FIGURE 10 3 Synthesis and rearrangement of secondary sugar allyltins. 

Trost and coworkers developed a chiral zinc phenoxide for the asymmetric aldol reaction of acetophenone or hydroxyacetophenone with aldehydes (equations 62 and 63) . This method does not involve the prior activation of the carbonyls to silyl enol ethers as in the Mukaiyama aldol reactions. Shibasaki and coworkers employed titanium phenoxide derived from a phenoxy sugar for the asymmetric cyanosilylation of ketones (equation 64). 2-Hydroxy-2 -amino-l,l -binaphthyl was employed in the asymmetric carbonyl addition of diethylzinc , and a 2 -mercapto derivative in the asymmetric reduction of ketones and carbonyl allylation using allyltin ° . ... 

Application of allyltin derivatives in organic synthesis is well documented [46-48]. Although the reports on the use of normal allyltins appeared already in the 1970s, the sugar analogs were introduced to the chemical literature almost two decades later. In 1988, Mortlock and Thomas reported the first preparation of such compound derived from glyceraldehyde [49]. Soon after that first paper, we proposed the synthesis of more complex organometallics from D-hexoses [41, 50]. 

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