Aldehyde from acetals

HOfCHjljOH, AI2O3, PhCH3 or CCI4, heat, 24 h, 80-100% yield. These conditions are selective for the formation of acetals from aldehydes in the presence of ketones. 

In 1992, Oda et al. reported a one-pot synthesis of optically active cyanohydrin acetates from aldehydes, which were converted to the corresponding racemic cyanohydrins through transhydrocyanation with acetone cyanohydrin, catalyzed by a a strongly basic anion-exchange resin [46]. The racemic cyanohydrins were acetylated by a lipase from P. cepacia (Amano) with isopropenyl acetate as the acyl donor. The reversible nature of the base-catalyzed transhydrocyanation enabled continuous racemization of the unreacted cyanohydrins, thereby effecting a total conversion (Figure 4.21). 

Inagaki, M. Hiratake, J. Nishioka, T Oda, J. One-pot synthesis of optically active cyanohydrin acetates from aldehydes via lipase-catalyzed kinetic resolution coupled with in situ formation and racemization of cyanohydrins. J. Org. Chem. 1992, 57, 5643-5649. 

Leonard NM, Oswald MC, Freiberg DA, Nattier BA, Smith RC, Mohan RS (2002) A simple and versatile method for the synthesis of acetals from aldehydes and ketones using bismuth triflate. J Org Chem 67 5202-5207... 

Anzalone PW, Baru AR, Danielson EM, Hayes PD, Nguyen MP, Panico AF, Smith RC, Mohan RS (2005) Bismuth compounds in organic synthesis a one-pot synthesis of homoallyl ethers and homoallyl acetates from aldehydes catalyzed by bismuth triflate. J Org Chem 70 2091-2096... 

A number of syntheses have been proposed, mainly from a-chlorosulfides and alcohols or from 0,0-acetals or 5,5-acetals. Many references on these methods are to be found in a paper dealing with a direct synthesis of 0,5-acetals from aldehydes [56],... 

Inagaki M, Hiratake J, Nishioka T, Oda J (1991) Lipase-catalyzed kinetic resolution with in situ racemization one-pot synthesis of optically active cyanohydrin acetates from aldehydes. J Am Chem Soc 113 9360-9361... 

All the foregoing syntheses of 0,0,0-orthoesters required at least two steps because 0,0,0-orthoesters cannot usually be prepared directly from esters by reaction with alcohols under add conditions analogous to the preparation of acetals from aldehydes and ketones. There are some exceptions.237 -239 For example. reaction of the racemic mixture of cis- and fraftf-lactones in Scheme 2.115 with (/ ,/ )-butane-2,3-diol in refluxing benzene afforded a mixture of four diastereoisomeric orthoesters (99%) in the ratio 6 6 1 1 that could be sepa-... 

Acetals from aldehydes or ketones and secondary alcohols. The synthesis of ketone di-rcc-alkyl acetals ordinarily proceeds in low yield. Roelofsen and van Bekkum report that such acetals can be prepared in 70 90% yield by use of type 5A molecular sieves to absorb selectively the water formed. p-Toluenesulfonic acid is used as the acid catalyst. 

ROH AdE2 then Sjsjl Acetal from aldehyde Ketal from ketone C OR... 

The use of methyl sulfoxide as the solvent and boron trifluoride etherate as the catalyst has been explored,29 and has given good yields of acetals from aldehydes (but not ketones). The procedure does suffer from certain disadvantages, in particular, the laborious removal of the solvent by vacuum distillation, and the fact that some anomerization may result when glycosides are so treated. 

Therefore only three examples for the use of surfactant templated mesoporous oxides in catalytic applications shall be highlighted here. More encompassing reviews on their catalytic properties can be found in two review articles [31,32] The first study elegantly used the combination of a suitable acid site strength and the influence of the regular mesopore system for the preparation of acetals from aldehydes [33]. MCM-41 was found to be superior to zeolites and amorphous... 

The system TMSOTf/2,6-lutidine has been proved to be highly effective for the deprotection of cyclic and acyclic acetals from aldehydes (eq 99) on the other hand, high chemoselectivity has been achieved when using triethylsilyl triflate/2,6-lutidine, which can deprotect acetals in the presence of ketals. ... 

De SK, Gibbs RA (2004) Ruthenium(III) chloride-catalyzed chemoselective synthesis of acetals from aldehydes. Tetrahedron Lett 45(44) 8141-8144... 

Hemiacetal he-me- a-s9- tal (1893) n. Any class of compounds characterized by the grouping C(OH)(OR) where R is an alkyl group and usually formed as intermediates in the preparation of acetals from aldehydes or ketones. Morrison RT, Boyd RN (1992) Organic chemistry, 6th edn. Prentice-Hall, Englewood Cliffs, NJ. 

FIGURE 17.27 The conversion of an ester into an ortho ester is analogous to the formation of acetals from aldehydes and ketones. 

The following reagents may also be used for the preparation of acetals from aldehydes and alcohols ... 

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