Relative reactivities of cyclic ketene acetals via cationic 1,2-vinyl addition copolymerization1

The relationship between the relative reactivities of ten cyclic ketene acetals and their structures was determined via cationic copolymerizations of eight different monomer pairs. Thus, 2-methylene-1,3-dioxolane (1) was copolymerized with 2-methylene-4-methyl-1,3-dioxolane (2), 2-methylene-4,5-dimethyl-1,3-dioxolane (3), 2-methylene-4,4,5,5-tetramethyl-1,3-dioxolane (4), 2-methylene-4-phenyl-1,3-dioxolane (5), and 2-methylene-4-(t-butyl)-1,3-dioxolane (6). Also 2-methylene-1,3-dioxane (7) was copolymerized with 2-methylene-4-methyl-1,3-dioxane (8), 2-methylene-4,4,6-trimethyl-1,3-dioxane (9), and 2-methylene-4-isopropyl-5,5-dimethyl-1,3-dioxane (10). The relative reactivities of these monomers are: 3 > 5 > 4 > 2 > 1 > 6; and 10 > 9 > 8 > 7. In spite of steric demands, substituents at the 4- or 5-positions in 2-methylene-1,3-dioxolane and substituents at the 4- or 6-positions in 2-methylene-1,3-dioxane serve to increase the copolymerization reactivity. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2841–2852, 1999     

Kinetic and thermodynamic control in the cationic copolymerization of cyclic ethers

Cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols proceeds, at the properly chosen conditions, with complete conversion of both comonomers and leads to telechelic oligodiols. These conditions are based on the simultaneous kinetic and thermodynamic control for two operating mechanisms namely active chain end and activated monomer mechanism. Kinetics of copolymerization and model reactions were studied. The ratios of rate constants of competing reactions, governing the copolymer composition, were determined and it was found, that the microstructure of the copolymer can be controlled at low conversion while at higher conversion the kinetics of the competing parallel reactions is not favourable for the formation of a regular copolymer, in contrast to the previously studied copolymerization of tetrahydrofuran with epichlorohydrin.     

Stereoselective synthesis of cyclic ethers via bromine assistedepoxide ring expansion

9-Oxabicyclo[6.1.O]non-4-ene reacts with bromine to give stereoselectively trans, trans-2,6-dibromo-9-oxabicyclo[3.3.1]nonane and trans, trans-2,5-dibromo-9-oxabicyclo[4.2.1]nonane.     

Correlation of cationic copolymerization parameters of cyclic ethers,formals, and esters

Carefully determined cationic copolymerization parameters of cyclic ethers, formals, and esters are collected. Relative reactivity correlates with basicity and free energy. Further correlations of the copolymerization parameters for styrene, the effect of promoters, and the known mechanism of hydrolysis permitted a decision between the carbonium ion (including acylium ion) or the oxonium ion as the active intermediate of the propagation. Structural features which promote depropagation are identified. Equations describing these possibilities were derived and briefly discussed. Catalyst and solvent effects limited the correlation possibilities.     

Regiospecific cationic polymerization of spiroorthoesters with different cyclic ether ring sizes

Spiroorthoesters (SOEs), cis‐2,3‐tetramethylene‐1,4,6‐trioxaspiro[4,5]decane ( I ) and cis‐2,3‐tetramethylene‐1,4,6‐trioxaspiro[4,6]undecane ( II ), with different cyclic ether ring sizes were synthesized, and their stereostructure and steric energy were determined. With steric‐hindrance‐sensitized 9‐phenyl‐9,10‐dihydro‐anthracen‐10‐ylium cation as an initiator, I and II underwent regiospecific polymerization to yield trans form of stereoregular poly(ether esters)—poly(trans‐2‐oxycyclohexyl pentanoate) (? [trans‐2‐OCHP]_n? ) ( III ) and poly(trans‐2‐oxycyclohexyl hexanoate) (? [trans‐2‐OCHH]_n? ) ( V ), respectively. With SnCl₄ as another initiator, I and II underwent regiospecific polymerization through different mechanisms to afford cis form poly(cis‐2‐oxycyclohexyl pentanoate) (? [cis‐2‐OCHP]_n? ) ( IV ) and trans form (? [trans‐2‐OCHH]_n? ) ( VI ) stereoregular poly(ether esters). The polymerization mechanisms of SOEs proceeded in the regiospecific manner were determined by the relationship among the sterostructures of SOEs and its subsequently formed polymers, the steric energy of monomers, and the free energy difference in the transition state of reaction. Owing to the conversion of cis substitution at C‐2 and C‐3 in I or II to the trans form during polymerization, polymers III , V , and VI exhibited a higher volume of expansion during polymerization than IV , which showed high volume shrinkage. Group contributions of divalent trans‐ and cis‐1.2‐cyclohexyl groups were derived and confirmed by measuring the densities of the corresponding stereoregular polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of cyclic ethers via 5-exo iodonium assisted epoxide ring expansion.

The transannular cyclization of (Z,Z)-1-hydroxy-cyclonona-2,6-diene by iodonium assisted oxirane ring expansion was studied. The regioselectivity for the [4.3.1] vs [5.2.1] 10-oxabicyclo decane skeletons is high, and the iodine addition is also highly trans-selective. The results are rationalized in terms of a tricyclic oxonium ion intermediate.     

Relative reactivities of phosphites in reactions with hydrotrioxides

Studies of the interaction of hydrotrioxides ROOOH of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1,1-dimetoxyethane, 1,1-diethoxyethane, benzaldehyde and tetrahydrofuran with trimethyl triisopropyl, tributyl, triallyl, triphenyl and tri-o-chresyl phosphites (RO)₃P have revealed that in mild conditions ROOOH rapidly and selectively oxidizes (RO)₃P to the corresponding phosphates. The reaction stoichiometry has been established. Aromatic phosphites are shown to be of inferior reactivity to ROOOH as compared with aliphatic phosphites.

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, 1-, 2-, 1-, 2-, 1,1-, 1,1-, -, -, -, -, -, -, -- (RO)₃P. ROOOH (RO)₃P . . , ROOOH .

     

Dilithiated synthons: synthesis of cyclic ethers

Recent advances in the generation of dilithiated synthons by arene-catalyzed lithiation of the corresponding dichloro compounds in the presence of carbonyl compounds (Barbier-type reaction conditions) as the key step are described. Further cyclization of the generated diols under different reaction conditions affords a variety of mono-, bi-, and spirocyclic ethers.     

Medium ring ethers by ring expansion-ring contraction: synthesis of lauthisan

[reaction: see text] A new general method for the construction of medium ring ethers has been developed. This involves the ring expansion of halo-O,S-acetals followed by a Ramburg-B?cklund ring contraction reaction with concomitant extrusion of the sulfur atom. This methodology has been utilized for the synthesis of cis- and trans-lauthisan.     

Medium-sized carbocycles by a zirconocene-catalyzed tandem formal ring expansion-magnesation reaction of alkenyl-substituted cyclic enol ethers

A new regio- and stereoselective zirconocene-catalyzed reaction for the synthesis of medium-sized rings is described. The global reaction supposes a formal ring expansion of a cyclic enol ether to give a functionalized carbocycle.     

Living cationic polymerization of isobutyl vinyl ether by EtAlCl2 in the presence of ether additives: Cyclic ethers,cyclic formals,and acyclic ethers with oxyethylene units

The living cationic polymerization of isobutyl vinyl ether (IBVE) was investigated in the presence of various cyclic and acyclic ethers with 1-(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃, 1 ]/EtAlCl₂ initiating system in hexane at 0°C. In particular, the effect of the basicity and steric hindrance of the ethers on the living nature and the polymerization rate was studied. The polymerization in the presence of a wide variety of cyclic ethers [tetrahydrofuran (THF), tetrahydropyran (THP), oxepane, 1,4-dioxane] and cyclic formals (1,3-dioxolane, 1,3-dioxane) gave living polymers with a very narrow molecular weight distribution (MWD) (M?_ω/M?_n ≤ 1.1). On the other hand, propylene oxide and oxetane additives resulted in no polymerization, whereas 1,3,5-trioxane gave the nonliving polymer with a broader MWD. The polymerization rates were dependent on the number of oxygen and ring sizes, which were related to the basicity and the steric hindrance. The order of the apparent polymerization rates in the presence of cyclic ether and formal additives was as follows: nonadditive ～ 1,3,5-trioxane ? 1,3-dioxane > 1,3-dioxolane ? 1,4-dioxane ? THP > oxepane ? THF ? oxetane, propylene oxide ? 0. The polymerization in the presence of the cyclic formals was much faster than that of the cyclic ethers: for example, the apparent propagation rate constant k in the presence of 1,3-dioxolane was 10³ times larger than that in the presence of THF. Another series of experiments showed that acyclic ethers with oxyethylene units were effective as additives for the living polymerization with 1 /EtAlCl₂ initiating system in hexane at 0°C. The polymers obtained in the presence of ethylene glycol diethyl ether and diethylene glycol diethyle ether had very narrow molecular weight distribution (M?_ω/M?_n ≤ 1.1), and the M?_n was directly proportional to the monomer conversion. The polymerization behavior was quite different in the polymerization rates and the MWD of the obtained polymers from that in the presence of diethyl ether. These results suggested the polydentate-type interaction or the alternate interaction of two or three ether oxygens in oxyethylene units with the propagating carbocation, to permit the living polymerization of IBVE. © 1994 John Wiley & Sons, Inc.     

Living cationic polymerization of vinyl ethers with a naphthyl group: Decisive effect of the substituted position on naphthalene ring

Living cationic polymerization of a vinyl ether with a naphthyl group [2‐(2‐naphthoxy)ethyl vinyl ether, βNpOVE] was achieved using base‐assisting initiating systems with a Lewis acid. The Et_1.5AlCl_1.5/1,4‐dioxane or ethyl acetate system induced the living cationic polymerization of βNpOVE in toluene at 0 °C. The living nature of this reaction was confirmed by a monomer addition experiment, followed by ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) analyses. In contrast, the polymerization of αNpOVE was not fully controlled; under similar conditions, it produced polymers with broad molecular weight distributions. The ¹H NMR and MALDI‐TOF‐MS spectra of the resultant poly(αNpOVE) revealed that the products had undesirable structures derived from Friedel–Crafts alkylation. The higher reactivity of αNpOVE in electrophilic substitution reactions, such as the Friedel–Crafts reaction, was attributable to the greater electron density of the naphthyl ring, which was calculated based on frontier orbital theory. The naphthyl groups significantly affected the properties of the resultant polymer. For example, the glass transition temperatures (T_g) of poly(NpOVE)s are higher by approximately 40 °C than that of poly(2‐phenoxyethyl vinyl ether). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Controlled cationic alternating copolymerization of various enol ethers and benzaldehyde derivatives: Effects of enol ether structures

Significant structural effects of enol ether monomers were demonstrated in cationic alternating copolymerizations with benzaldehyde derivatives (BzAs). α‐Methyl, β‐methyl, β,β‐dimethyl, and cyclic enol ethers were copolymerized with BzAs by the EtSO₃H/GaCl₃ system with 1,4‐dioxane in toluene at ?78 °C. β‐Methyl and cyclic monomers, β‐monosubstituted compounds, induced copolymerizations with BzAs, some of which were well controlled to yield alternating copolymers with controlled molecular weights (MWs) and narrow MW distributions. Conversely, an α‐methyl vinyl ether (VE) did not copolymerize with BzAs at all, probably due to its high reactivity and unfavorable ketal linkage formations. In addition, a β,β‐dimethyl VE underwent only cyclotrimerizations because of its larger steric repulsion. The product alternating copolymers, especially those with cyclic units, exhibited improved thermal properties compared to those with simple VEs units. Under appropriate conditions, the alternating copolymers selectively degraded into the corresponding cinnamaldehyde derivatives by acid hydrolysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1334–1343     

Relative reactivities of 1,2-cyclohexadiene with conjugated dienes and styrene

Generation of 1,2-cyclohexadiene in the presence of conjugated dienes leads to (2 + 2) and/or (2 + 4) cycloaddition products. Methods used to generate 1,2-cyclohexadiene were: (1) treatment of 6,6-dibromobicyclo[3.1.0]hexane with methyllithium in tetrahydrofuran-ether at 0° and 60°; (2) treatment of 1,6-dichlorocyclohexene with magnesium in tetrahydrofuran at 60°; and (3) treatment of 1-bromocyclohexene with t-BuOK in THF at 60° or dimethyl sulfoxide at 40°. Comparison of relative reactivities with various dienes and styrene in ether solvents at 60° confirmed that the same intermediate, uncomplexed 1,2-cyclohexadiene, was involved in these reactions. Relative reactivities at 0° and 60° were found to be: 2-methylfuran (0·12, 0·14); furan (0·17, 0·16); 2,4-hexadiene (0·17,—); cis-pentadiene (0·53, 0·53); 2,3-dimethylbutadiene (2·35, 1·9); 1,3-cyclohexadiene (1·85,—); styrene (2·35, 1·9); and 1,3-cyclopentadiene (47, 14).