Cyclohexylidene ketal

Methylene A cetals Ethylidene Acetals BenzyUdene A cetals Substituted BenzyUdene Acetals Isopropylidene Ketals Cyclohexylidene and Other Ketals Cyclic Orthoesters... 

The cyclohexylidene ketal, prepared from a catechol and cyclohexanone (AI2O3/ TsOH, CH2CI2, reflux, 36 h), is stable to metalation conditions (RX/BuLi) that cleave aiyl methyl ethers. The ketal is cleaved by acidic hydrolysis (coned. HCl/ EtOH, reflux, 1.5 h, 20°, 12 h) it is stable to milder acidic hydrolysis that cleaves tetrahydropyranyl ethers (1 AHCl/EtOH, reflux, 5 h, 91% yield). ... 

Cyclopentylidene Ketal, i Cyclohexylidene Ketal, ii Cycloheptylidene Ketal, iii... 

These problems were circumvented by protecting the C(4),C(5) diol prior to Wittig olefination step (Figure 3). Thus, treatment of 10b (a mixture of pyranose and furanose anomers prepared by hydrolysis of 8 with aqueous trifluoroacetic acid) with excess EtSH and concentrated HCI (as solvent) at provided dithioacetal 9 in 50% yield, along with 25% of a mixture of thiopyranosides and thiofuranosides that was recycled to 10b in high yield by treatment with HgCIa and CaCOa in aqueous CH3CN. Finally, the diol unit was protected as a cyclohexylidene ketal, and then the thioacetal was hydrolyzed under oxidative conditions to arrive at the key aldehyde intermediate 3. 

The reaction of the cyclohexylidene ketal 3 of a chiral inline, prepared from L-threonine, gives a single adduct (4), which is converted by known reactions into Jty/o-daunosamine (5). 

Other ketals which are frequently used if a modified acid stability is wanted are the cyclopentylidene, the cyclohexylidene and the cycloheptylidene ketals. They are readily prepared by the reaction of a diol and the cycloalkanone in toe presence of ethyl orthoformate and mesitylenesulfonic acid. The relative rates of their acid-catalyzed hydrolysis are given in Scheme 50. 

The cyclohexylidene ketal has been prepared from dimethoxycyclohexane and TsOH HC(OEt)3, cyclohexanone, TsOH,EtOAc, heat, 5h, 78% l-(trimethylsiloxy)-cyclohexene, coned. HCl, 20°C, 10-30 min, 70-75% yield, cyclohexanone, TsOH, CUSO4/ , and 1-ethoxycyclohexene, TsOH, DMF. The cyclohexylidene derivative of a fra .v-l,2-diol has been prepared. Cyclohexylidene ketals may also be prepared directly from an epoxide with MTO catalysis. ... 

Cyclohexylidene and isopropylidene monoketals 47 and diketals 48, 49, and 50 are well-known protected myo-inositol derivatives (Scheme 3-1). Compounds 47 ketalized at the 1,2-cis-positions have been utilized conveniently for the synthesis of various inositol phosphates since 47 can be regioselectively functionalized and prepared in good yield by the conventional ketalization procedure and subsequent partial deprotection of the less stable trans-type ketals from the diketal mixture formed first in the reaction.22 Three diketals S have been also often employed for the synthesis of target inositol derivatives, because they have the following advantages (1) A trans vicinal hydroxyl moiety as well as the 1,2-... 

The relative reactivity of the four free hydroxyl groups in 1,2-ketals 47 of myo-inositol can be estimated based on the reports of several substitution reactions with acyl chlorides and chlorosilanes. The reaction of 1,2-cyclohexylidene-myo-inositol 47a... 

Higher homolog 1,3-polyols are prepared by an iterative procedure (Scheme 88). Acetonide 601 is first protected as the cyclohexylidene ketal 604. Selective deprotection of the acetonide affords diol 605 in 42% yield, along with unreacted 604 (yield = 89% based on consumed starting material). Conversion of 605 to epoxide 606 followed by reaction of 606 with lithiated 598 in a procedure similar to the sequence outlined in Scheme 87 ultimately produces polyol 607 with 95 5 syn selectivity. 

Cyclohexanone, 2-(1-cyclohexen-1-yl)-. See 2-Cyclohexenyl cyclohexanone Cyclohexanone, 2-cyclohexyl-. See Cyclohexylcyclohexanone Cyclohexanone, 2-cyclohexylidene-. See 2-Cyclohexylidenecyclohexanone Cyclohexanone diethyl acetal CAS 1670-47-9 El NECS/ELINCS 216-798-0 Synonyms Cyclohexanone diethyl ketal 1,1-Diethoxycyclohexane Empiricai C10H20O2... 

Perhaps classical for the protection of 1,2- and 1,3-cis-diols is the isopropyl-idene (acetonide) function. This acid labile ketal may be formed by reaction of a ribonucleoside with acetone in the presence of an acid (HCl, p-toluene-sulfonic, H2SO4) and water scavenger (2,2-dimethoxypropane, ethyl orthoformate). Other similar protecting groups include the benzylidene and cyclohexylidene functions. 

Cyclohexylidene is the only ketal system besides isopropylidene which has been used to any extent as a protecting group [126-128]. Cyclohexylidene derivatives have been prepared by allowing the glycol to react with cyclohexanone in the presence... 

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