Ketals compounds

During the LANA process, we observed the decomposition of 1,2/1,4 ketal (compound 2) in 2 hours in HPLC grade acetonitrile. A noticeable color change was observed. Since previous experience with sample decomposition led us to suspect that oxygen played a role in the decomposition reaction, a sample was prepared in acetonitrile with or without degassing. After 1 hour,... 

Figure 10 Ketalized compounds from moraceous plants...

Figure 11 The formation of the ketalized compounds from the original adducts under acidic conditions...

Z)-6-hetieicosen-I]-one Douglas-fir tussock moth (Orgyia p.ieudotsuf ata) S Lewis acid induced C-O bond cleavage of a bicyclic ketal compound using AcCl-NaF [188] [189] ... 

Ketones form hemiketals upon reaction with alcohols. Because of the —COH group, hemiketal compounds display the properties of alcohols and can react further with alcohols to form ketal compounds which have the properties of ethers. 

According to the second equation, 1 mole of acetone produces 1 mole of ketal compound, so (1 - x) mole of acetone produces (1 - x) mole of ketal compound. 

A wide variety of 4,7-dihydro-l,3-dioxepins or l,3-dioxep-5-enes are known (1, 2). These cyclic acetal or ketal compounds are conveniently prepared by the acid catalyzed reaction of cis-2-1 Current address University of Wisconsin, Madison, WI53706. 

Problem 14.20. Write equations to show the reactions of benzaldehyde and butanone with excess methanol. Show both the hemiacetal (hemiketal) and acetal (ketal) compounds. 

Compound I is a ketal, compound II is a hemiacetal, compound III is a hemiketal, compound IV is something else (triether), and compound V is an acetal. 

For the synthetic application of this method to Erythrina alkaloids, Anh Tuan and Kim [56] reinvestigated the palladium catalyzed cyclization of the requisite precursor which could be formed from the condensation of ketoester 43 and bromo-arylamine 44. In the reaction, two main products were formed. When the intermediate 45 was treated with Pd(OAc)2 in DBU, an enol intermediate (46) was formed in 30% yield through y-lactam enolate formation followed by cyclization. Some amoimt of the eorresponding ketal compound, the precursor of the enol intermediate, could be obtained if the reaction process was quenched earlier. Treatment of 46 with TsOH in acetone afforded compound 47 in 71% yield. Reduction of the carbonyl compound 47 under Luche condition, affording a mixture of diasteromers in a 2.6 1 ratio, was followed by elimination to afford the known intermediate (48) for erysotramidine (49) in 64% yield. 

Ketal Tosylates. The second candidate for the acid proliferation is ketal derivatives having a tosylated residue (5). These were synthesized by the ketalization of benzoylacetate, followed by LAH reduction and tosylation (5). Compound 5 (mp 48-50 C) had to be stored in a refrigerator since crystals of 5 were converted into black materials gradually at an ambient temperature upon prolonged storage. The ketal compound (5) was readily converted in the present of an addic spedes into p-keto-tosylate (6) which is subjected to the -elimination to give TsOH in a non-linear maimer (Scheme 2(b)). NMR spectra of a solution of 5 in the presence of TsCH at 100 revealed that e p-keto-tosylate (6) as an intermediate was formed during the reaction (6). 

Structures of mulberrofurans F (131), G (27), and K (179) have been established by correlation with chalcomoracin (103) and with mul-berrofuran C (130) using a ketalization reaction 91, 112). Therefore, the configuration of the three chiral centers in the methylcyclohexene ring of the ketal compounds is the same as those of 103 and 130. 

The structure of an orthoester reminds us of that of acetals and ketals, compounds that are easily cleaved by dilute acids. The mechanism of hydrolysis for orthoester 4 should be similar to that of the acetals and ketals, starting with the protonation of one of the oxygen atoms and followed by the formation of a carbo-cation greatly stabilized by resonance. The overall process is a SnI mechanism that ends up by addition of water. Two different species 8 and 10 can be formed... 

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