1.3- Dioxepane

3-dioxepane, (iH2 —O—CHj —O—CH2 —CH2 —. They propose a ring expansion mechanism similar to the one they suggested for 1,3-dioxolane. Again they find an equilibrium polymerization, this time with a ceiling temperature of +27°C for a 1 molar solution. = —3.6 0.3 kcal mole and ASss = H-5 1.5 cal deg mole .  

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With aldehydes or their derivatives, butanediol forms acetals, either 7-membered rings (1,3-dioxepanes) or linear polyacetals the rings and chains are easily intraconverted (126,127). 

Dioxepanes 63 were hydrolyzed with aqueous hydrochloric acid to the starting diol. A thionyl chloride promoted ring-opening of dioxepane 63 to intermediate 64 has been reported. When treated with base, compound 64 can be transformed into vinylic ether 65 in 58% yield (81ZOR1047) (Scheme 31). 3-Methylfurazan-4-acetic acid was converted to the vinyl derivative 66 via an esterification, reduction, mesylation, and base elimination sequence (81JHC1247) (Scheme 31). 

C8H12N2 99-98-9) see Methylthioninium chloride 4-ainino-l,3-dimethylbenzene (CgH N 95-6S-7) see Picotamide (5K,6S)-6-aniino-2,2-dimethyl-l,3-dioxepan-5-ol acetate (salt)... 

Ring-opening polymerization of 2-methylene-l,3-dioxepane (Fig. 6) represents the single example of a free radical polymerization route to PCL (51). Initiation with AIBN at SO C afforded PCL with a of 42,000 in 59% yield. While this monomer is not commercially available, the advantage of this method is that it may be used to obtain otherwise inaccessible copolymers. As an example, copolymerization with vinyl monomers has afforded copolymers of e-caprolactone with styrene, 4-vinylanisole, methyl methacrylate, and vinyl acetate. 

FIGURE 6 Synthesis of PCL by the free radical polymerization of 2-methylene-l,3-dioxepane. (From Ref. 51.)... 

Bailey, W, J., Ni, Z., and Wu, S.-R., Synthesis of poly-e-capralactone via a free radical mechanism. Free radical ringopening polymerization of 2-methylene-l, 3-dioxepane, J. Polym. Sci., Polym. Chem. Ed.. 3021-3030, 1982. 

By utilizing a combination of RAFT and cationic ROP, the synthesis of [poly(methyl methacrylate)][poly(l,3-dioxepane)][polystyrene] miktoarm star terpolymers was achieved [182], The approach involved the synthesis of PS functionalized with a dithiobenzoate group by RAFT polymerization and subsequent reaction with hydroxyethylene cinnamate (Scheme 98). The newly created hydroxyl group was then used for the cationic ring opening polymerization of 1,3-dioxepane (DOP). The remaining dithiobenzoate group was used for the RAFT polymerization of methyl methacrylate. 

A third example combines cationic ROP and ATRP for the synthesis of (polytetrahydrofurane)(poly-l,3-dioxepane)(PS) miktoarm stars (Scheme 99). The initiating sites for the above polymerization were created step-by-step from amino-succinic acid (Scheme 99). 

These representative aliphatic polyesters are often used in copolymerized form in various combinations, for example, poly(lactide-co-glycolide) (PLGA) [66-68] and poly(lactide-co-caprolactone) [69-73], to improve degradation rates, mechanical properties, processability, and solubility by reducing crystallinity. Other monomers such as 1,4-dioxepan-5-one (DXO) [74—76], 1,4-dioxane-2-one [77], and trimethylene carbonate (TMC) [28] (Fig. 2) have also been used as comonomers to improve the hydrophobicity of the aliphatic polyesters as well as their degradability and mechanical properties. 

The base-catalysed ring contraction of 1,3-dioxepanes offers an attractive route to 4-formyl tetrahydropyrans (Scheme 14) , whilst fused exo-cyclic dienes 27 result from the radical cyclisation of alkenyl iodides 26 (Scheme 15) <00OL2011>. Intramolecular radical addition to vinylogous sulfonates is highly stereoselective, leading to the ci s-2,6-disubstituted tetrahydropyran (Scheme 16) . 

There are relatively few entries in the non-fused dioxepin area, and most of these focus on reactions of these systems. For example the triflic acid-initiated polymerisation of 1,3-dioxepane in the presence of acetic acid and hexanedicarboxylic acid has been studied and mechanistic aspects discussed <00JPS(A)1232>. Biodegradable microspheres for the controlled delivery of drugs have been made from copolymers and homopolymer blends of L-lactide and l,5-dioxepan-2-one <00PP1628>. Ring contraction of 5-methylene-l,3-dioxepanes (eg. Ill) on reaction with trimethylsilyl trifluoromethanesulfonate in the presence of base afforded the exo tetrahydropyrans, in good yields <00TL2171>. 

Synthetically, 5-chIoro-2,2,5-trimethyl-l,2-dioxepane can be accessed by T1CI4-mediated cyclization of an unsaturated monoperoxyacetal through a 7-endo/endo pathway in modest yield <00JOC8407>. 

A high level of activity continues in connection with the synthesis of antimalarial artemisinin analogues and congeners, in which the 1,2-dioxepane moiety is embedded. Recent examples include the syntheses of various 10-substituted deoxoartemisinins of type 123 (eg. R1 = Cl COMe) from dihydroartemisinin acetate, and of type 124 (eg. R2 = a-OH, R3 = Me), from Grignard reagent addition to 10-(2-oxoethyl)deoxoartemisinin . 

P2t Z = 2 Dx = 1.281 R = 0.06 for 1,338 intensities. The molecule contains a seven-membered, 1,3-dioxepane ring which has a conformation close to the twist-chair, with a two-fold axis through the mid-... 

For the polymerisation of 1,3-dioxolan and 1,3-dioxepan by HC104 Plesch and Westermann [20] were able to show by conductivity measurement that Xxr = [HClO4]0 and hence obtained values of kp These values are probably composite, and the contributions from k v and k"p are not known, but is has been explained in Section 3 that they are unlikely to differ by more than one power of ten. 

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