Oxiranyl ethers, rearrangement

While allyl and glycidyl ethers are converted into a mixture of oxetane and oxepine products with xec-butyllithium, Mordini and co-workers reported that allyl, benzyl, and propargyl epoxy ethers can be regioselectively converted into 2-vinyl, 2-phenyl, or 2-aIkynyl-3-(hydroxyalkyl) oxetanes upon treatment with either Schlosser s base or other mixed metal bases. Some of the best results were obtained with the LDA/potassium ferf-butoxide mixture (LIDAKOR, ref 194). While rearrangement of propargylic or benzylic epoxide ethers formed exclusively the four-membered oxetanes, rearrangements of allyl oxiranyl ethers show a selectivity for cyclization to the seven-membered ring. Trialkylsilyl-substituted epoxide allyl ethers also show a preference for the oxepine, and mixtures are obtained as the size of the silyl substituents is increased (Scheme 17). 

Tricyclic oxiranyl-substituted cyclobutanone 7 rearranged quantitatively to bicyclic tetrahy-drooxepin 8 on treatment with boron trifluoride-diethyl ether complex in chloroform.225... 

A stereoselective approach to tetrasubstituted (Z)-/3-hydroxy-o -TMS (trimethylsi-lyl)enol ethers occurs via a sequential addition/[ 1,2]-Brook rearrangement/epoxide-opening process of TMS-substituted oxiranyl anions with acylsilanes (Scheme 46). ... 

A stereoselective approach to tetrasubstituted (ii)-/ -hydroxy silyl enol ethers from aryl-substituted oxiranyl anions and acylsilanes is reported to occur via a sequential addition - [l,2]-Brook rearrangement - epoxide-opening (Scheme 87). ... 

---