Unsaturated, Cyclic Compounds

Direct elimination from C-2 and C-3 of glycosyl derivatives offers another means of preparing compounds of this class, and the best known member, methyl 4,6-0-benzylidene-2,3-dideoxy-a-o-cn/ /iro-hex-2-enoside 

The reaction of epoxides of carbohydrates with methylmagnesium iodide gives mainly deoxyiodo alcohols which, on p-toluenesulfonylation, afford derivatives []for example, methyl 4,6-0-benzylidene-3-deoxy-3-iodo-2-0-p-tolylsulfonyl-a-D-glucoside (74), prepared from methyl 2,3-anhydro-4,6-0-benzylidene-at-D-allopyranoside ] which imdergo ready elimination when treated with sodium iodide in acetone (Route A). The general applicability of this route to unsaturated compounds has been noted, and, in the pentose series, it has been applied to the preparation of methyl 4-0-benzyl-2,3-dideoxy- 3-L-glj/cero-pent-2-enoside (79). Here, the elimination occurs much 

The esters of deoxy compounds, used in Routes B and C, are prepared either from the products of reductive cleavage of epoxides, or from deoxy sugar derivatives synthesized by some other specific route. Sulfonyloxy substituents are eliminated in a basic medium or, as in the reaction of methyl 4,6-0-benzylidene-3-deoxy-2-0-p-tolylsulfonyl-a-D-aro6mo-hexo-side (75) (73), by heating the compound with soda-lime. In the carbo- 

Epoxides have been converted into olefins by heating with trimethyl phosphite, but methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside was recovered unchanged after this treatment.The corresponding episulfide, methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-epithio-a-n-alloside (77), however, reacts to give the unsaturated glycoside (73) (Route D), 

A sixth route to the 2,3-alkene (73) has now been reported,involving the treatment of methyl 4,6-0-benzylidene-2,3-di-0-(methylsulfonyl)-a-D-glucopyranoside with potassium ethylxanthate in boiling 1-butanol. In addition,methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside gives rise to (73) on similar treatment. Yet another method of introducing a double bond into a carbohydrate ring involves the conversion of a 1,2-cis-diol into an alkene grouping by way of the derived thionocarbonate. By this means, benzyl 4-0-benzyl-2,3,6-trideoxy- 3-L-er2/ /iro-hex-2-enoside has been prepared (see also pp. 118,127). 

Synthetic work has utilized, in the main, the base-catalyzed eliminations noted previously,1 and a series of compounds having the general structure 40 have now been synthesized as outlined in Table II. 

Attempts to prepare compounds of this group by heating the derived 2, 3 -thionocarbonates with trimethyl phosphite have not met with the same success. From 5 -0-trityluridine, the 2,2 -anhydro-nucleoside was produced, instead of the cyclic ester, by treatment 

Unsaturated Nucleosides (40) and Their Synthesis from 2-Deoxy-D-err/thro- or -threo-pentofuranosyl Nucleoside Derivatives 

Adenine OH D-erythro-, 3 -p-toluenesulfonate sodium ethoxide in EtOH 63 

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Similarly to alkenes, alkynes react with various titanium-methylidene precursors, such as the Tebbe reagent [13,63], titanacydobutanes [9b, 64], and dimethyltitanocene [65] to form the titanium-containing unsaturated cyclic compounds, titanacydobutenes 67 (Scheme 14.29). Alternatively, 2,3-diphenyltitanacydobutene can be prepared by the reaction of the complex titanocene(II) bis(trimethylphosphine) with 1,2-diphenylcyclopropene [66]. Substituent effects in titanacydobutenes [67], the preparation of titanocene-vinylke-tene complexes by carbonylation of titanacydobutenes [68], and titanacyclobutene-vinylcar-bene complex interconversion [69] have been investigated. 

The unsaturated cyclic compounds 32 and 33 show none of the absorption characteristics of the open-chain analog, cis-stilbene, since the 7 electrons of the benzene rings and the C=C bonds cannot overlap because of the rigid architecture of the molecules. 

Cyclic olefins and diolefins form much more aerosol than 1-alkenes that have the same number of carbon atoms (for example, cyclohexene 1-hexene, and 1,7-octadiene 1-octene). The same effect of chain length and double-bond position is observed for diolefins (1,7-octadiene > 1,6-heptadiene > 1,5-hexadiene, and 1,7-octadiene 2,6-octadiene). Heavier unsaturated cyclic compounds, such as indene and terpenes, form even more aerosol. 

Aromatic hydrocarbons are unsaturated cyclic compounds that are resistant to addition reactions. The aromatic hydrocarbons derive their name from the distinctive odors they exhibited when discovered. Benzene is the most important aromatic compound. Because many other aromatic compounds are derived from benzene, it can be considered the parent of other aromatic compounds. Benzene molecular formula is... 

Only occasionally are compounds with unsaturated carbohydrate components found in Nature. A well-known example is blasticidin S (3) which inhibits blast disease of rice,3 and a most unusual case is that of a 2,6-dideoxy-trisaccharide glycal (1,2-unsaturated cyclic compound) isolated from a plant in India.4... 

Boron Attached to Other Unsaturated Cyclic Compounds... 

Recent developments in the chemistry of the 1,2-unsaturated cyclic compounds, namely, the glycals and the 2-hydroxyglycals, are included in order to supplement the earlier Chapters on these topics. There follows a discussion of other cyclic and acyclic sugars which possess, at various positions in the carbon chain, alkenyl, enolic, or enamine systems. The scope has been arbitrarily restricted by the exclusion of the ends themselves [and, therefore, of reductones and compoimds related directly to L-ascorbic acid (1)], of such enones as the pyrone derivative (2), and of dienes or dienones [for example, kojic acid (3)]. Cyclohexene derivatives... 

VII. 5,6-Unsaturated Cyclic Compounds 1. Furanoid Alkene Derivatives... 

The foregoing schemes prove that the intermediate product formed when acetic anhydride is used consists of a mixture of two unsaturated cyclic compounds, both containing the linkage... 

Electrocyclic reactions are a class of pericyclic reactions in which a conjugated polyene interconverts with an unsaturated cyclic compound containing one less carbon-carbon double bond than the polyene. " The reactions can be promoted thermally or photochemically and take place with a very high degree of stereoselectivity. 

Syntheses of l Unsaturated Cyclic Compounds and Related Derivatives -... 

Syntheses of 3,4-Unsaturated Cyclic Compounds - Compound 30, available in three steps from 5-hydroxymethyl-l,6-anhydro-a-L-a//ro-hexopyranose was converted into ewMevoglucosenone by reaction with copper-quinoline (decarboxylation at C-5), zirconium oxide induced olefination at C-3 (reductive decarboxylation) then deacylation and oxidation. The 5-hydroxymethyl analogue of ent-levogluco-senone was also made from the same starting materials. ... 

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