Glucal derivatives

Scheme 32 Benzannulation with glucal-derived chromium carbenes...

N. Pravdic, I. Franjic-Mihalic, and B. Danilov, An improved synthesis of a 2-acetamido-D-glucal derivative, Carbohydr. Res., 45 (1975) 302-306. 

I. Marco-Contelles and J. Ruiz-Caro, Iridoids from carbohydrates via Pauson-Khand reaction synthesis of advanced highly oxygenated cyclopentane-annulated pyranosides from D-glucal derivatives,. /. Org. Chem., 64 (1999) 8302-8310. 

By far the best studied of these compounds is n-glucal, derived from D-glucose (and D-mannose). This compound and its derivatives and reactions will be considered in detail below the description of the glycals from other sugars can then be presented in more concise form. 

Smolyakova, IP, Smit, W A, Zal chenko, E A, Chizhov, O S, Shashkov, A S, Arenesulfenyl chloride adducts of glucal derivatives in the preparation of C-glucosides, Tetrahedron Lett., 34, 3047-3050, 1993. 

The synthesis of the required compound 61 commenced with the D-glucal derivative 57 (Scheme 11.16), the cyclopropanation of which gave the (3-derivative 58 as the major compound [63]. Opening the latter gave the intermediate mercurio derivative 59, which was reduced to 60. Final mesylation at the anomeric center followed by spontaneous elimination yielded the branched-glycal 61. This compound was in turn debenzylated [62]. 

As shown in Scheme 11.84, glucal derivative 409 was oxidized to the corresponding aldehyde, which was treated with the lithium derivative of phenylacetylene to give a mixture of alcohols protected as their acetates 410. lodoglycosylation of the glycal with 4-methoxybenzyl alcohol gave... 

An l-hydroxy-l,2-benziodoxol-3(17/)-one 1-oxide (IBX)-mediated process provides another efficient and stereoselective preparative route for the s)uithesis of amino sugars. For example, reaction of the D-glucal derivative 113 with p-methoxybenzene isocyanate in the presence of a catalytic amount of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by treatment with IBX furnishes the cyclic carbonate 115, through urethane 114. Subsequent removal of the p-methoxybenzyl (PMB) protecting group by CAN affords the protected amino sugar 116 (O Scheme 56) [94]. 

Indeed, pent-l-enitols [225], glucal derivatives [226], and galactal and fucal analogs have all been obtained via l-en-3-ones by using the above-mentioned approach. Thermal cyclocondensation of aldehyde 117 with diene 118 gave racemic enone 119 (O Scheme 41), which is used as a s)uithon in the preparation of the rifamycin S chain [227]. 

Another approach developed by the Vogel group relies on a carbonylative Stille cross-coupling between stannylated glucal derivative 410 and enol triflate 412 derived from isolevoglucosenone [152] (O Scheme 80). 

The most recently reported route to the D-arabinofmanose ring nucleus involves an oxidative cleavage of protected glucal derivatives as illustrated in Figure 12 [74]. 

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