Chemoselective isomerization of amide-substituted oxetanes with Lewis acid to give oxazine derivatives or bicyclic amide acetals

Monomer-Isomerization Polymerization of 3-Methyl-3-(phthalimidomethyl)oxetane with Two Different Ring-Opening Courses

“…Many polyethers having various pendant groups have been so far synthesized by the cationic ring-opening polymerization of the corresponding functionalized oxetanes. Because of the high nucleophilicity of the cyclic ether, the propagation of electrophilic growing species can proceed even in the presence of other functional groups such as olefin, ether, ester, ketone, nitrile, amide, imide, azo, sulfonate, as already exemplified in our work. , However, a few exceptions have been reported in the Lewis acid-catalyzed reactions of oxetanes carrying a γ-carbonyl-containing functional group at the 3-position. − Corey et al observed the first example of ortho ester synthesis from ester-substituted oxetanes 5a. Recently, we have found the intramolecular acetalization of cyclic imide-substituted oxetanes 6 and the chemoselective isomerization of amide-substituted oxetanes .…”

“…Because of the high nucleophilicity of the cyclic ether, the propagation of electrophilic growing species can proceed even in the presence of other functional groups such as olefin, ether, ester, ketone, nitrile, amide, imide, azo, sulfonate, as already exemplified in our work. , However, a few exceptions have been reported in the Lewis acid-catalyzed reactions of oxetanes carrying a γ-carbonyl-containing functional group at the 3-position. − Corey et al observed the first example of ortho ester synthesis from ester-substituted oxetanes 5a. Recently, we have found the intramolecular acetalization of cyclic imide-substituted oxetanes 6 and the chemoselective isomerization of amide-substituted oxetanes . In these isomerizations, accessibility between the oxonium α-carbon atoms and the carbonyl oxygen atoms (relatively 1,6-positioned) renders the intramolecular nucleophilic attack preferable .…”

Substituent Effect on the Cationic Monomer-Isomerization Polymerization of (Cyclic Imide)-Substituted Oxetanes with Two Different Ring-Opening Routes

“…Subsequently, ring closure of 1,3-oxazin-2-ylium cation B gives 2 as an oxonium form C. The intervention of B has been strongly supported by the fact that the closely related isomerization of secondary amide-substituted oxetanes afforded 4H-dihydro-1,3-oxazine derivatives, as shown in Scheme 5. [5] The difference in the isomerization products could be attributed to differences in stability between intermediate cations B and B9. The X-ray absolute structures of 2 a and 2 d showed an approximately coplanar arrangement of six atoms constituting a C1N(1C)1C(2O)1C linkage, indicating that the nitrogen atom possesses an almost complete amide character.…”

“…[2,3] As shown in Scheme 1, 1a undergoes a Lewis acid-catalyzed isomerization to give bicyclic acetal (2 a) prior to polymerization, because accessibility between the oxonium a-carbon atom and the carbonyl oxygen atom (relatively 1,6-positioned) renders the intramolecular nucleophilic attack preferable. [4,5] Subsequently, 2 a polymerizes cationically in either a single or double ring-opening manner depending on the temperature, to give two polymers with different structures. One is a polyacetal (3 a) containing tetrahydro-1,3-oxazine rings in the main chain, and the other is a polyether (4 a) Full Paper: This study reports the effect of substituent on the cationic monomer-isomerization ring-opening polymerization of 3-(R 1 -methyl)-substituted 3-R 2 -oxetanes (1), in which R 1 is phthalimide, maleimide, succinimide, or glutarimide, and R 2 is ethyl, benzyl, phenyl, or isopropyl.…”

Cationic Monomer-Isomerization Polymerization of Oxetanes Having an Ester Substituent, to Give Poly(orthoester) or Polyether

“…As outlined in Scheme 1, the isomerization can be viewed as chemoselective transformation of the oxetanes into other heterocyclic compounds: oxetane imides to bicyclic acetals (Equation (2)), [5] and oxetane sec-amides to substituted 5,6-dihydro-4H-1,3-oxazines (Equation (3)). [6] Oxetane tert-amides bring about a similar single isomerization to bicyclic acetals (Equation (4)), [6] or alternatively, a double isomerization via ring expansion to bicyclic acetals and ring contraction to give different 4-membered azetidine derivatives at higher temperatures (Equation (5)). [7] Full Paper: This study shows the cationic monomer-isomerization polymerization of 3-R 1 -oxetanes (1) having a 3-ester substituent (1CH 2 OCOR 2 ) through two ring-opening routes (R 1 = CH 3 , Ph; R 2 = Pr, Ph).…”