1.3- Dioxolanylium ions

Other examples of formation of esters from 1,3-dioxolanylium ions were reported for the D-ribofuranose series156 (see Section III,6,a), and formation of halogeno derivatives has been described for 1,6-an-hydro-/3-D-glycopyranoses.157... 

C-3 (or C-4) from a 1,3-dioxolane actually, this reaction (see Section HI, 14) was observed for 2,2-disubstituted 1,3-dioxolanes, and it may be assumed that, if there is any competition between removal of a proton from C-2 and from C-3 (or C-4), the rate of the first reaction is far greater than that of the second. The possibility of dioxolanylium ions reacting with nucleophilic reagents was first demonstrated by Hanes-sian and Staub,152 and the scope of these reactions was independently investigated by Pedersen and coworkers.153-157 Hanessian and Staub152 treated methyl 5-0-benzoyl-2,3-0-benzylidene-j3-D-ribofuranoside (125) with triphenylmethyl fluoroborate in acetonitrile, and obtained, after hydrolysis, a 1 1 mixture of the two benzoates 127 and 128 (yield 83%), probably through the benzoxonium ion 126. The same reaction... 

For discussions and papers related to dioxolanylium ions and their rearrangements, see, for instance, Refs. Ill and 139. 

Meerwein was the first to succeed in obtaining dioxolanylium ions of type 2, sufficiently stabilized as salts with non-polarizable anions that they could be isolated crystalline. The compounds can be prepared by splitting out of an anion from cyclic ortho esters or acetals wherein the required ring-system is already present. The ortho ester 1 reacts with antimony pentachloride or boron trifluoride, with splitting out of OR, to give 2. Acetals (3) from aldehydes can be converted, by hydride abstraction with triphenylmethyl or triethyl-oxonium fluorohorate, into salts (2) this reaction proceeds well only with acetals of the 1,3-dioxolane type (3) that have little steric hindrance. With acetals of the 1,3-dioxane type, formed from aldehydes, the reaction of hydride abstraction is not, as a rule, possible. In all such reactions, the anion involved is either SbClg or BF4 . 

S. Jacobsen, I. Lundt, and C. Pedersen, Investigation of the stability of dioxolanylium ions derived from 1,5-anhydro-D-arabinitol, Acta Chem. Scand., 21 (1973) 453 60. 

S. Jacobsen and C. Pedersen, Dioxolanylium ions derived from carbohydrates. I. Reactions with water and with bromide ions, Acta Chem. Scand., B28 (1974) 866-872. 

Chlorodiphenoxymethane as well as 1,3-dioxolanylium salts ° react with suitable cyanides to give the corresponding nitriles (429) and (430) (Scheme 78), respectively. The cyanodioxolanes (430) can serve as cyanide carriers to noncylic carboxonium ions giving, for example, diethoxyacetonitrile (431). ... 

In the following discussion, the dioxolanylium (2) and dioxanylium ring-systems will be referred to simply as acyloxonium derivatives, as the carboxonium ion of the ring is formally derived from a carboxylic acid. Thus, system 2 is an acetoxonium salt when R = Me, and a benzoxonium salt when R = Ph. 

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