Diacetals cyclic

Aroxyacoxy compds. Bis(hemiacetals), cyclic 1-Carbalkoxyoxonium salts Diacetals, cyclic a-Diketone monoketals Enolperoxides a-Hydroxyacetals... 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cij-cyclopentene-3,5-diacetate (129) affords the furan derivative 131 [87]. The C- and 0-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into c -3-hydroxy-4-cyanocyclopentene (134)[S8]. Similarly, chiral m-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of yV-tosylcarbamate[89]. 

When enantiomerically pure fni/is-2-acetoxycyclohexyl tosylate is solvolyzed, tiie product is racemic /mn -diacetate. This is consistent with the proposed mechanism, since the acetoxonium intennediate is achiral and can only give rise to racemic material. Additional evidence for diis interpretation comes from the isolation of a cyclic ortho ester when the solvolysis is carried out in ethanol. In this solvent the acetoxonium ion is captured by the solvent. 

C23HJ2O, 1250-97-1) see Halopredone diacetate (liP)-21-(acetyloxy)-ll,17-dihydroxypregn-5-ene-3,20-di-one cyclic 3,20-bis(l,2-ethanediyl acetal)... 

Several cyclic glyphosate analogs related to this series were described previously as intermediates to prepare glyphosate. These include various N-phosphonomethylhydantoins and diketopiperazines. A more extended glyphosate piperazine analog 106 has also been prepared firom the Mannich reaction of ethylenediamine-lV,lV -diacetic acid (65). 

Although several more examples of this type of ring system are known in the literature, the majority of these are cyclic diacetals, which have been used for the protection of diols. These have not been included in this chapter the reader is directed to the chapters dealing with the relevant diols. 

The diacetoxylation works well with a number of cyclic and acyclic conjugated dienes and has been applied to the synthesis of natural products33,34. For example, the meso diacetate from 2,4-hexadiene was used for the enantiodivergent synthesis of the carpenter bee pheromone343. 

Kinetic resolution ofallylic alcohols. The (R)- and (S)-BINAP-Ru diacetate complexes can resolve racemic allylic alcohols, both acyclic and cyclic, with high enantiomeric selectivity. Thus hydrogenation of ( )-2 catalyzed by (S)-l at 76% conversion provides (S)-2 (>99% ee) and anti-3 (49 1, 39% ee). Hydrogenation of (S)-2 catalyzed by either (R)- or (S)-l provides anti-3 (>23 1). Similar results obtain with ( )-4. 

This elimination fails with diacetates of enediols and involves an overall cis-elimination in cyclic systems. 

In solution, the 170 NMR spectra of tributyltin acetate and dibutyltin diacetate show a single signal in a variety of solvents over the range 200-300 K. This is interpreted to imply the existence, in solution, of a cyclic monomer in which the carboxylate groups ate anisobidentate, and are undergoing rapid intramolecular exchange 34.350... 

Competition Experiments of Ley Ley examined product distributions to obtain relative reactivity values (RRVs) for both rhamnose and mannose sugars with benzyl, 3,4-cyclic diacetals, and benzoyl groups. Using a limiting amount of acceptor (1 equiv), two donors were added in excess (2 equiv each), followed by the addition of activator (NIS/TfOH, 2 equiv) (Scheme 11.13). After quenching the reaction, the product distribution was analyzed by -NMR. 

Scheme 11.13 Production distribution in a reaction with rhamnose and mannose sugars with benzyl, 3,4-cyclic diacetals, and benzoyl groups.

Further research within in our laboratory has illustrated that certain substrates bearing trans-hydroxyl groups can be directly protected using cyclic and acyclic diones, thus alleviating the requirement for prior formation of the tetramethoxydiacetals.6 For example, butane-2,3-dione has proved particularly useful for the preparation of butane diacetal (BDA) derivatives, which serve as useful alternatives to cyclohexane diacetal (CDA) derivatives. 

Metal-catalyzed allylic substitution reactions have been a mainstay of synthetic chemistry because of their ability to proceed irreversibly and with high selectivity [42]. It is also feasible, however, to produce analogous systems that are completely reversible and nonselective, or ideally situated for use in DCC. These are essentially metal-catalyzed transesterification reactions, with the added feature of potentially providing stereochemical scrambling (and selection) as well as constitutional variation. An early example of this was provided in 2000 by Kaiser and Sanders [43]. In the absence of a template, reaction of diallyl diacetate 22 with a dicarboxylic acid in the presence of catalytic Pd(0) produced a negligible amount of the cycfized compound 23 (Fig. 1.9). However, when templated with 1,3-bis(4-pyridyl) benzene, yield of the cyclic structure increased to roughly 10%, independent of the dicarboxylic acid used. 

Only short comments will be given for other acetal derivatives that are less popular Chart 1 presents a list of formulae of cyclic acetals, mainly, those with five- and six-membered rings (1,3-dioxolanes and 1,3-dioxanes). Seven-membered ring acetals are omitted because they are scarcely represented in carbohydrate chemistry. The special case of spiroacetah and cydohexane-l,2-diacetal-protecting groups, which have been reported recently, will be presented in Part K. 

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