3.4- Di-O-acetyl-L-rhamnal

SCHEME 9. Ferrier rearrangement by glycosidation of 3,4-di-O-acetyl-L-rhamnal with several alcohols catalyzed by Montmorillonite K-10. 

The d- and L-enanatiomers of rhodinose and amicetose specifically labeled with deuterium at C-2 and C-3 were prepared from the same synthon.274 Starting from 3,4-di-O-acetyl-L-rhamnal, (2S,3f )-[2,3-2H2]-L-rhodinosc was synthesized as shown in Scheme 58. 

Further support for the HS AB-based rationalization comes also from later studies demonstrating that making sulfur harder (5 -alkyl to S-acetyl) dramatically alters regioselectivity and leads to 2,3-unsaturated products [176,177]. In the reaction from 3,4-di-O-acetyl-L-rhamnal 87 with thioacetic acid or potassium thioacetate in the presence of BF3 -Et20, only products substituted at C-1 88 and 89 were isolated (O Scheme 30) [177]. 

Di-O-acetyl-L-rhamnal (27) has been rearranged to the 2-ene (28) from which 2,3,6-trideoxy-L-erythro- and L-f/ireo-hexopyranosides are available. ... 

Last year saw the application of D-xylose to the synthesis of sesbanimide and this strategy has been extended to encompass ring C variants. A new synthesis of the cosmetic component 70 (a well-studied synthetic target that is derived from the civit cat) from 3,4-di-O-acetyl-L-rhamnal has been developed and the same group have described the use of L-rhamnal for synthesis of L-oleandrose 71. Methyl 6-deoxy-2,3-0-isopropylidene-a—D-mannopyranoside provides a flexible precursor to a series of deoxysugars (tetrahydropyrans), a-D-amicetoside 72, a-D-perosaminoside 73 and a-D-janoside 74.49... 

The reaction of furan with 3,4-di-O-acetyl-L-rhamnal gave epimeric (40) and 1-C-(2-furyl)-hex-2-enopyranose (41). Compound (40) could be converted into 2-deoxyglycosides, e.g. (42), and to 3 -deamino-3 -C-(2-furyl) daunorubicins. 

Di-O-acetyl-L-rhamnal (115) gave a mixture of (220) (60%), (221) (5%), and (222) (22%) when treated with sodium azide in acetonitrile in the presence of boron trifluoride etherate. The conversion of the epimeric 3-azides (220) into derivatives of L-acosamine and L-ristosamine is noted in Chapter 8. 

Di-O-acetyl-L-rhamnal 37 with a C-4 acetoxy group equatorial also in the preferred (l) conformation has a smaller dipole moment and shows therefore a... 

Addition of trifluoromethyl oxyfluoride to 3,4-di-(9-acetyl-L-rhamnal led to a synthesis of 2-deoxy-2-fluoro-L-glucose and -L-rhamnose, whilst a similar reaction with 3,4-di-O-acetyl-L-fucal was used to prepare 2-deoxy-2-fluoro-L-... 

The stereochemistry of the addition of chlorine to 3,4-dihydro-2/f-pyran has been found to be influenced by the polarity of the solvent in which the reaction is conducted. Stereoselective syn addition occurred in non-polar solvents e.g. n-pent-ane) to give a mixture of cis- and rrans-2,3-dichlorotetrahydropyrans in the ratio of ca. 4 1, whereas the ratio was 1 2 in polar solvents e.g. dichloromethane). cis-2,3-Dichlorotetrahydropyran yielded exclusively trans-products with various nucleophiles (N3, MeO, PhS, and AcO ) in DMF with inversion of configuration at C-2, whereas trans-2,3-dichlorotetrahydropyran yielded the cis-product with the thiophenate anion and a mixture of cis- and trans-products with the other anions. Hydrogen chloride and hydrogen bromide added to 3,4-di-O-acetyl-L-fucal (134) and -rhamnal (135) to give adducts (136) and (137), respectively, possessing the a-L configuration. ... 

Also 2 -halo-3 -hydroxy derivatives of various anthracyclinones show a high activity against P 388 mouse leukemia in certain in-vivo tests. A compound like 98 has been prepared in the 2-deoxy-2-iodo-a-L-ma no-series by Horton et al. [59, 60] starting from di-O-acetyl-L-rhamnal (28). Similarly, Thiem et al. have also successfully prepared the tetracenomycinone-C glycoside 99 [61]. From 4-0-acetyl-3-0-(p-methoxy)-benzyl-L-fucal (102) the glycoside derivatives 103 and 104 in the talo-series were obtained. 

The 6-deoxy-L-talose derivative 14 was the major product of osmium mtroxide hydroxylation of the alkene 13, itself prepared from di-O-acetyl-L-rhamnal by allylic rearrangement followed by Mitsunobu inversion at C-4.U 6-Deoxy-D- ructose and 6-deoxy-L-sorbose were obtained as a separable mixture from the transketolase-catalysed reaction of hydroxypyruvate with 2,3-dihydroxybuQialdehyde (mixture of isomers) (Scheme 4). ... 

A new way of converting acylated glycals into 2,3-unsaturated glycosides involves treatment with alcohols in acetonitrile in the presence of catalytic amounts of DDQ (Scheme 4). Efficiencies are good and the anomeric selectivities (mainly a) seem to be very similar to those obtained when this type of reaction is conducted with Lewis acid catalysts. Di-O-acetyl-L-rhamnal is the source of tfie glycosylating agents 11, suitable furanoid compounds for making ristosamine related products. ... 

KOH) has afforded a high yield of methyl 6-chl(nx>4,6-dideoxy-a-D-iy/o-hexopyranoside. Di-0-acetyl-L-rhamnal in the presence of chlorine, silver acetate and methanol has generated a 30% yield of methyl 3,4-di-0-acetyl-2-chloro 2-deoxy-a-L-riiamnopyranoside which was one of the chlorinated derivatives used in the synthesis of chlorodeoxy analogues of a-L-Rhap-(l->3) a-L-Rh p-(l- 3)- -D-GlcNAqp-1-O-Me. ... 

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