From Cycloheptatriene

SCHEME 13.108a Hudlicky s syntheses of tetrose, pentose and hexose derivatives. 

Swem oxidation, provides enone 476. After reduction of ketone 476 to the ally lie alcohol, ozonolysis and reduction give triol 477, which is oxidatively cleaved to 2,3 4,5-di-0-isopropylidene-L-glucose. On treatment with acid, L-glucose is released [213a]. 

Alcohol 470 was also converted to 3-deoxy-D-araZ m6 -heptulosonic acid [213b] and to enantio pure 2-deoxyhexoses [213c]. Cycloheptatrienone (tropone) has been converted into heptitol derivatives via the optical resolution of the (tropone)Fe(CO)3 complex [213d]. 

SCHEME 13.108b BanwelTs total syntheses of KDN, NeuSAc and Vitamin C. 

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The Hiickel rule predicts aromaticity for the six-7c-electron cation derived from cycloheptatriene by hydride abstraction and antiaromaticity for the planar eight-rc-electron anion that would be formed by deprotonation. The cation is indeed very stable, with a P Cr+ of -1-4.7. ° Salts containing the cation can be isolated as a product of a variety of preparative procedures. On the other hand, the pK of cycloheptatriene has been estimated at 36. ° This value is similar to those of normal 1,4-dienes and does not indicate strong destabilization. Thus, the seven-membered eight-rc-electron anion is probably nonplanar. This would be similar to the situation in the nonplanar eight-rc-electron hydrocarbon, cyclooctatetraene. 

Although the chemistry of zirconium in its lower oxidation states is still relatively unexplored, it is developing. Examples which offer the possibility of further exploitation include the blue, paramagnetic zirconium(III) compound 32) [L2Zr(/r-Cl)2ZrL2] L = C5H3(SiMe3)2-l,3, and the sandwich and half-sandwich compounds derived from cycloheptatriene red... 

Heterocyclic Fused Tropylium Salts from Cycloheptatrienes AND Triphenylcarbenium Salts (Scheme 52)... 

The tropylium cation is prepared easily by transfer of a hydride ion from cycloheptatriene to triphenylmethyl cation in sulfur dioxide solution. This reaction is related to the hydride ion transfer, (CH3)3C + RH —> (CH3)3CH + R , discussed in Section 10-9 ... 

In addition to their reactions with alkenes and carbanions as nucleophiles benzhydryl cations react with hydride donors.282 284 These hydride transfer reactions show the same linear dependence of log k upon E as the reactions with alkenes and the same constant relative selectivity, that is with slopes of plots close to 1.0, for structures ranging from cycloheptatriene to the... 

The highly crowded tris( 1 -naphthyl)methyl cation 150 and tris(2-naphthyl)methyl cation 151 were prepared and used to abstract hydride ion from cycloheptatriene to generate tropylium ion.363 Hydride abstraction, however, could be performed only with the less crowded cation 150. 

Another aromatic molecule containing six n electrons is C7H7+, the tropylium ion, derived from cycloheptatriene. This positive ion forms fewer complexes than does benzene, and they are less thoroughly studied. A molecule that has 10 electrons and has an aromatic structure is the cyclooctatetraenyl ion, C8H82. Some sandwich compounds containing this ligand are known as well as complexes of the type... 

Phenyl-1,3-dithiolium or 1,3-benzodithiolium cations abstract hydride from cycloheptatriene, giving the thermodynamically more stable tropylium salt and 4-phenyl-l,3-dithiole or 1,3-benzodithiole. ... 

Similar arguments can be used to predict the relative stabilities of the cycloheptatrienyl cation, radical, and anion. Removal of a hydrogen from cycloheptatriene can generate the six-vr-electron cation, the seven-ir-electron radical, or the eight-ir-electron anion (Figure 15.7, p. 572). Once again, all three species have numerous resonance forms, but Huckel s rule predicts that only the six-vr-electron cycloheptatrienyl cation should be aromatic. The seven-or-electron cycloheptatrienyl radical and the eight-or-electron anion are antiaromatic. 

Scialdone, M.A., and Johnson, C.R., Building blocks for skipped polyols, syn-1,3-Acetonides by chemoenzymatic synthesis from cycloheptatriene. Tetrahedron Lett., 36, 43, 1995. 

A variety of diverse synthetic methods have been empioyed for the preparation of cyclopropane (1 j. Schlatter and Demjanov and Dojarenko pyrolyzed cyclopropyltrimethylammonium hydroxide at 320°C using platinized asbestos as the catalyst. About equal amounts of cyclopropene (1) and cyclopropyidimethylamine are formed, contaminated with some dimethyl ether and ethylene. Treatment with dilute hydrochloric acid removed the amine from the gas stream and 1 was separated from the other products by gas chromatography. Alder-Rickert cleavage of the Diels-Alder adduct formed from cycloheptatriene and dimethyl acetylenedicarboxylate resulted only in the formation of a polymer and trace amounts of 1. A simple approach by Closs and Krantz based on the synthesis of 1-methylcyclopropene involved the addition of allyl chioride to a suspension of sodium amide in mineral oil at 80°C. Under the conditions employed, 1 could readily escape from the reaction mixture. Though a number of variations were tried, the yield of 1 never exceeded 10%. 

Cyclopentadiene is only a slightly weaker acid than water. The eqnilibrium for its deprotonation is more favorable than for other hydrocarbons becanse cyclopentadienide anion is aromatic. The contrast is striking when we compare this eqnilibrium with that for loss of a proton from cycloheptatriene. 

Unlike cyclopentadiene, cycloheptatriene is not an acidic hydrocarbon its pK is about 36. If a proton could be abstracted from cycloheptatriene, the resulting anion would have eight it-electrons and would be an unstable, anti-aromatic system. 

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