1.4- Dioxacycloalkane

The decarboxylation of clavulanic acid and its methyl ether has been accomplished using mercury(li) acetate, albeit in low yield. The anodic oxidation of -oxocarboxylate cyclic acetals (32) in anhydrous methanol gives 2-methoxy-1,4-dioxacycloalkanes (33) in 40—60% yield. A systematic study of the anodic oxidation of /3-keto carboxylate anions has also appeared. ... 

Thus the range of bicyclic peroxides available via peroxymercuration may be quite limited. Nevertheless where the method works best, namely with 1,5- and 1,4-cyclo-octadiene, it makes a valuable contribution in that each peroxymercuration is regiospecific and leads to a dioxabicyclodecane that is isomeric with the [4.2.2] compound 23 available via photooxygenation (Eq. 18). Furthermore, the [3.3.2] compounds derived from 1,5-cyclooctadiene are, to the best of our knowledge, the only bicyclic peroxides obtained to date that do not contain either a 5- or a 6-membered dioxacycloalkane ring. 

Dioxacycloalkanes In the case of 1,3-dioxacyloalkanes, there are two possibilities for the rupture of the C-O bond. Esters or diol monoethers can be prepared depending on the regioselectivity of the bond rupture (Scheme 4.11). 

Dioxacycloalkanes are cyclic acetals that are used frequently as protective groups. Substituted derivatives have been synthesized to achieve easy removal. Simplest of all, the 4-phenyl-1,3-dioxolane has not been used commonly because cleavage needs electrolytic conditions. A mild hydrogenolysis method was developed in 1997 to make this protective group more popular (Scheme... 

In the previous section I have described some researches which originated from me wishing to test certain alleged observations and various ideas which seemed questionable, and therefore that work has mainly a reactive character. In the present section I will outline some proactive researches, that is investigations which started with me at Keele and which initiated new lines of enquiry. It so happens that many of the researches of this type were concerned with the polymerisation of dioxacycloalkanes, the properties of oxonium ions, the polarography of carbenium and oxonium ions and various kinds of BIE, and they therefore fall outside the scope of this review but there were enough proactive researches on alkenes to make a story of steadily evolving ideas. 

A Some of the most interesting and informative experiments in this field were done by Pepper s group and then at Keele and elsewhere with anhydrous perchloric acid as the initiator. It is therefore historically important that in the present super-cautious, safety conscious era, few, if any, workers are ever likely to follow Pepper s pioneering work with this hazardous material, to test the reproducibility of these classical findings. The same applies of course to our studies on the polymerisation of various 1,3-dioxacycloalkanes, most of which were also done with anhydrous HC104, see Chapter 7. There is no substitute for it, as every acid behaves differently and in particular the lazy worker s substitute aq. HC104 + acetic anydride, is a very different initiator system. 

Some Aspects of the Polymerisation of 1,3-Dioxacycloalkanes, P. H. Plesch, Pure and Applied Chemistry, 1976, 48, 287-293. 

The Propagating Species in the Polymerisation of 1,3-Dioxacycloalkanes by Perchloric Acid (1975)... 

The object of the work described was to discriminate between the two principal rival theories concerning the polymerisation of 1,3-dioxacycloalkanes by anhydrous perchloric acid, the Mainz theory and the Keele theory . By means of Jaaks s method for determining tertiary oxonium ions we found that in polymerisations under the driest conditions the concentration of these is negligibly small. This was done with 1,3-dioxolane (1), 4-methyl-l,3-dioxolane (4), and 1,3-dioxepane (5), and the findings are supported by determinations of the content of hydroxy groups of polymers prepared and killed under different conditions. 

The recent theory of Penzcek, which involves co-ordinated oxy-carbenium ions, is also shown not to be applicable to the systems considered here. The heuristic value of the ring-expansion theory is illustrated briefly by reference to a new method of synthesising crown ethers from 1,3-dioxacycloalkanes, which arose from it. 

In concluding this paper dedicated to our distinguished octogenarian, it is especially appropriate to mention the heuristic practical value which our ring-expansion theory has had, since he has always been intent upon applications and practical uses. It was the ring-expansion theory which led the senior author to imagine that the acid-catalysed reactions of cyclic formals with olefins would be insertion reactions [21]. In his view they involve the insertion of an olefin into the 0-1, C-2 bond of a protonated (or alkylated) 1,3-dioxacycloalkane ... 

In this way the unstable 1,3-dioxacycloalkanes and their oligomers would be converted into stable ethers. This has been proved experimentally, and the reaction offers some exciting synthetic possibilities [17, 18]. In particular, it provides a new route to a variety of new crown ethers, such as the l,4,7,10-tetraoxa-ll,ll-dimethylcyclotridecane (a 13-crown-[4]-ether) from isobutene and the formal of triethylene glycol but that is another story ... 

The Propagating Species in the Polymerisation of 1,3-Dioxacycloalkanes by Perchloric Acid, Y. Firat, F.R. Jones, P.H. Plesch and P.H. Westermann, Die Makromolekulare Chemie, Supplement 1, 1975, 203-216. 

Evidently, the types of compound compatible with this mixture are not many, but it has been used successfully for various 1,3-dioxacycloalkanes and hydrocarbons. It must not be used with halogen compounds although chloro- and bromo-alkanes can be dried safely over sodium films, provided that they are initially at least Grignard dry and free of oxygen. In the author s laboratory specimens of CHjClj and MeBr which had been over sodium films under vacuum for several years were analysed and found to contain only traces of the Wurtz-condensation products. 

Methyloxirane showed a complex pattern of transformations over various solid acids in a pulse microreactor study.728 Nafion-H was found to exhibit the highest activity (30% conversion at 90°C) to produce propanal (about 22% selectivity) and cyclic dimers (substituted 1,3-dioxacycloalkanes, 60% selectivity). 

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