Reactions with Cyclic Acetals

Acetals can be used as the solvent for organometallic compounds but in certain cases a Barbier-type reaction may take place (see Sect. 2.4.2 for intramolecular Barbier reactions with haloacetals). 

Tischtschenko, in 1887, first applied acetals in organometallic chemistry in an attempt to develop a general synthetic method for the preparation of primary alcohols [86]. 

Several years later Wagner and Ginzberg reported the use of oxymethylene in a Wagner-Saytzefif -type reaction with zinc and allyl iodide [87]  

Soon after the discovery of the Grignard reagent, Grignard and Tissier [88] synthesized primary alcohols by the reaction of organomagnesium halides with trioxymethylene . 

Fournier, a few years later [89], used the same cyclic acetal in a one-step procedure. No yields were reported of the products which were used as intermediates in the synthesis of carboxylic acids. 

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Reactive collision gases have also been used in organic MS. Pioneering experiments involved the study of the formation of an adduct ion between protonated esters and ammonia in the collision cell of a TQ instrument [50]. Since then, numerous examples have been reported such as the study of gas-phase reactions of dilactones, psorospermin, and quabalactone diterpenes [51], different phospholipid classes [52], ethyl vinyl ether, the transacetalization with gaseous caiboxonium and carbosulfonium ions by colhsion cell reactions with cyclic acetals and ketals [53], and ketalization of phosphonimn ions using 1,4-dioxane [54]. 

Reactions of cyclic acetals with organosilicon compounds 97MI42. 

In many cases, the yields of these products are high. However, the use of /V-silylated triazoles as nucleophiles or the use of cyclic nitroso acetals (475) substituted at the C-3 atom leads to a noticeable decrease in the yield of the oximes. Therefore, steric hindrance in nitroso acetals and a decrease in nucleophilicity of A-centered nucleophiles result in an increase in the contribution of side reactions. It should be emphasized that C -nucleophiles, such as anions of nitro compounds, are not involved in coupling reactions with cyclic nitroso acetals (475). However, the products, which formally correspond to the C,C-coupling mechanism, can be prepared by the nucleophilic substitution of chlorine in compound (476 d) by a Sa/2 mechanism (Scheme 3.254, product (483c), the yield was 79%). 

A masked allylic boron unit can be revealed through a transition-metal-catalyzed borylation reaction. For example, a one-pot borylation/allylation tandem process based on the borylation of various ketone-containing allylic acetates has been developed. The intramolecular allylboration step is very slow in DMSO, which is the usual solvent for these borylations of allylic acetates (see Eq. 33). The use of a non-coordinating solvent like toluene is more suitable for the overall process provided that an arsine or phosphine ligand is added to stabilize the active Pd(0) species during the borylation reaction. With cyclic ketones such as 136, the intramolecular allylation provides cis-fused bicyclic products in agreement with the involvement of the usual chairlike transition structure, 137 (Eq. 102). 

Trithia-[3]-peristylane 706, a novel Civ symmetric thiabowl, can be synthesized by the reaction of cyclic acetal 705 with LR. The acetal is derived by ozonolysis and subsequent acetalization of bullubalene (Scheme 107) <20040L1617>. 

In other systems (cyclic ethers, acetals, esters, amides, siloxanes), the branched ions participate in further reactions, sometimes (cyclic acetals, siloxanes) with the rates not much different than the rates of reaction of cyclic onium ion active species. 

With cyclic acetals and ketals, selective reductions allow the blocked hydroxy groups of the diol to be deprotected one at a time, a matter of some importance in carbohydrate chemistry. Although there have been a few studies of stereoselective reductions at the masked carbonium center of chiral ketals, more has been done with the formally related reactions in which C—C bonds are formed stereoselectively. ... 

Such chains might have a small probability of propagating by dissociation of the complex, but could also lead to the cyclic ketone above in a true termination reaction, or in the reaction with tritiated acetic acid. In the... 

The method most likely to provide information concerning the nature of the reaction intermediates is that of detailed, kinetic analysis under a variety of carefully controlled conditions. It is evident that, in the application of this method, there is an extensive field of investigation to be surveyed, not only of the action of acyl trifiuoroacetates on hydroxylic compounds under the influence of different media and catalysts, but also of the peculiar differences between the ring-opening reactions of cyclic acetals with this type of reagent and with that which is employed in the Hudson acetolysis procedure. 

The cationic polymerization of monomeric formaldehyde with cyclic acetals and ethers, which bypasses the stage of cyclic formaldehyde oligomer formation, has been known some time60,61. It was, considered difficult, however, to introduce a process of this kind into industry because of the high sensitivity of the reaction system to polar impurities. 

Hie cyclic anhydride (80.4) reacts with trimethylsilyi azide under anhydrous conditions to give a mixture of I,3-oxazine-2,6-dione isomers, which was used without further purification to synthesis several extended purines. Reaction with formamidine acetate in DMF in effect replaced the furandione ring by a pyrimidinone. Cyanamide produced a new fiued 2-aminopyrimidin-4-one [in (80.5, R = NH )], while urea led to a pyrimidinedione. Isatoic anhydride similarly yields 2-aminoquinazolin-4-one on treatment with cyanamide-DMF. 

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