Other Carbon-bonded Derivatives

Some C-platinum bonded compounds have been obtained as shown in 

The synthesis of 2-amino-2,6-dideoxy-D-glucopyranose-6-sulphonic acid, an analogue of a bacterial cell wall component, has been pre-pared via an acetylated 6-deoxy-6-thio compound. 

Treatment of l,2-0-isopropylidene-3,5-di-0-tosyl-a-D-xylofuranose with lithium diphenylarsinide has afforded 5-deoxy-l,2-0-isopropylidene-5-C-diphenylarsino-3-O-tosyl-a-D-xylofuranose, and the arsenic containing ribosides 19 have been prepared using standard procedures.  

The displacement of primary iodides in some carbohydrate derivatives by lithiated 2-trimethylsilyl-l,3-dithiane followed by hydrolysis of the dithioacetal has allowed the synthesis of some acylsilanes (e.g. 21 from 20), and a review on the oxidation of the carbon-silicon bond has included a number of carbohydrate examples.  

Lithium bis(dimethylphenylsilyl)cuprate and lithium methyl(dimethylphenyl-silyl)cuprate have been used to effect a conjugate addition of the dimethylphenyl-silyl moiety to some carbohydrate enones. Use of trimethylstannyl lithium and tributylstannyl lithium also afforded conjugate addition products. In a new approach to carbohydrate organotin compounds, tributylstannylcopper has been used as a source of nucleophilic tributyltin to effect displacements of a primary tosylate, an allylic bromide and addition to an aldehyde.  

Syntheses of l,2 3,4-di-0-isopropylidene-6-0-3-(triphenylstannyl)propyl-a-D-galactopyranose and 1,6-anhydro-3,4-0-isopropylidene-2-C -triphenylstannyl methyl-P-D-galactopyranose have been described as well as a family of [6-0-( 1,2 3,4-di-0-isopropylidene-a-D-galactopyranosyl)methyl]tin species Ph Sn-(CH20R)4 n (n = 1-3 ROH = l,2 3,4-di-0-isopropylidene-a-D-galacto-pyranose), and 1,2 3,4-di-0-isopropylidene-6-0- triphenylstannylmethyl - a- d -galactopyranose.  

The reaction of methyl 2,3-anhydro-4,6-0-benzylidene-o-D-mannopyranoside with Ph2AsLi gave rise to the corresponding 3-deoxy-3-C-diphenylarsino-altropyranoside, whereas methyl 2,3-anhydro-4,6-D-benzylidene-a-D-allopyra-noside with Ph2AsLi or PhsSnLi gave the corresponding 2-deoxy-2-C-diphenyl- 

Azidophenylselenylation of glycals has generated 2-azido-l,2-dideoxy-l-C-phenylselenyl compoimds, and a 4-deoxy-4-C-selenyl derivative has been used in the synthesis of disaccharides with Se in the interglycosidic linkage. A 

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Carbon-bonded Phosphorus Derivatives Other Carbon-bonded Derivatives Oxygen-bonded Derivatives... 

Double amidation of phosgene, to give symmetrical ureas, is considerably easier to perform. Considerable interest is attached to the recent reaction of imidazole with phosgene, which led to l,T-carbonyldiimidazole, an extremely reactive compound on account of the lability of its amide bonds 597 The ease with which the imidazole group can be replaced by other groups offers the widest possibilities for synthesis of other carbonic acid derivatives, carboxylic esters, amides, and hydrazides, peptides, phosphoric esters, etc., all under the mildest conditions.598 Since l,T-carbonyldiimidazole is hydrolysed even by atmospheric moisture, it must be prepared under the most strictly anhydrous conditions. 

To identify the carbonyl compound and the ylide required to produce a given alkene mentally disconnect the double bond so that one of its carbons is derived from a car bonyl group and the other is derived from an ylide Taking styrene as a representative example we see that two such disconnections are possible either benzaldehyde or formaldehyde is an appropriate precursor... 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

The insertion of alkynes into a chromium-carbon double bond is not restricted to Fischer alkenylcarbene complexes. Numerous transformations of this kind have been performed with simple alkylcarbene complexes, from which unstable a,/J-unsaturated carbene complexes were formed in situ, and in turn underwent further reactions in several different ways. For example, reaction of the 1-me-thoxyethylidene complex 6a with the conjugated enyne-ketimines and -ketones 131 afforded pyrrole [92] and furan 134 derivatives [93], respectively. The alkyne-inserted intermediate 132 apparently undergoes 671-electrocyclization and reductive elimination to afford enol ether 133, which yields the cycloaddition product 134 via a subsequent hydrolysis (Scheme 28). This transformation also demonstrates that Fischer carbene complexes are highly selective in their reactivity toward alkynes in the presence of other multiple bonds (Table 6). 

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