Preparation and Structure of Novel Macrocyclic Oligoesters from 6,8-Dioxabicyclo[3.2.1]octan-7-one

Synthesis and ring-opening polymerization of bicyclic lactones containing a tetrahydropyran ring. 2,6-Dioxabicyclo[2.2.2]octan-3-one

“…Preparation of a Stereoisomer Mixture of Methyl 6-Methoxytetrahydropyran-3-carboxylate (8). A mixture of 5 (4.50 g, 0.019 mol), sodium chloride (1.29 g, 0.022 mol), water (0.68 g, 0.038 mol), and dimethyl sulfoxide (20 mL) was heated in a 50-mL round-bottomed flask fitted with a condenser.…”

Specific formation of a polymer containing five-membered oxalactone rings in the main chain in the cationic ring-opening polymerization of 6,8-dioxabicyclo[3.2.1]octan-7-one

“…The conversions of 1 into oligomers and polymer were estimated from gel permeation chromatogram of the reaction mixture after the reaction was terminated by the addition of a small amount of pyridine. At lower overall conversions (the first two runs in Table I), the products were mostly oligomeric materials with molecular weights Table I Polymerization of rac-6,8-Dioxabicyclo[3.2.1]octan-7-one (1) at 0 °C°o mer, solvent, time, lower higher yield/ M" X Mw X 0 Solvent, chloroform; initiator, BF3-OEt2, 5 mol % to monomer. 4 By gel permeation chromatography.…”

“…A possible isomerization mechanism is proposed in Scheme II: The isomerization is initiated by the addition of a cationic species R+ onto the oxygen atom of a tetrahydropyran ring (1) (upper right). The C-0+ bond of the tetrahydropyran ring is cleaved unimolecularly to give an oxacarbenium ion (lower right), to which the oxygen atom of the neighboring tetrahydropyran ring (2) attacks to form the oxonium ion of a five-membered oxalactone ring (1,3-dioxolan-4-one) structure (lower middle).…”

“…Cationic polymerization of a bicyclic oxalactone, 6,8dioxabicyclo[3.2.1 ]octan-7-one, is unique in that the racemic monomer (1) gives highly selectively 10-, 20-, and 25-membered macrocyclic oligoesters (dimer (2), tetramer (4), and pentamer ( 5)) in acetonitrile, chloroform, and 1-nitropropane, respectively, at -40 °C,1™3 while one of the enantiomers of 1, (+)-(lfi,5K)-6,8-dioxabicyclo[3.2.1]octan-7-one (IK) affords preferentially the optically active cyclic tetramer (4K) in acetonitrile and the optically active cyclic pentamer (5K) in 1-nitropropane.3™5 Furthermore, each cyclic oligoester derived from the racemic monomer 1 is not a mixture of cyclic oligomers of different structures but it is a single compound: The cyclic dimer 2 consists of a pair of enantiomeric monomeric units (IK and IS), and in contrast, the cyclic tetramer 4 and pentamer 5 are structurally identical with the optically active cyclic tetramer 4K and pentamer 5K, respectively, derived from the optically active monomer IK.6™8 In other words, 4 is an equimolar mixture of 4K and its enantiomer 4S, and 5 is an equimolar mixture of 5K and its enantiomer 5S. sr: (ir)5…”

Mechanistic aspects of selective formation of 10-, 20-, and 25-membered macrocyclic oligoesters in the cationic polymerization of 6,8-dioxabicyclo[3.2.1]octan-7-one

“…18 The composition of the reaction products was determined from the relative peak areas corrected for the differences in the refractive indices of the different compounds by a JASCO TRIROTAR gel permeation chromatograph (column, JASCO JSP101, 50 cm; eluent, chloroform). IR spectra were Polymerization of 6,8-Dioxabicyclo[3.2.l]octan-7-one 1181 propane.…”