Oxetenes synthesis

The first reliable synthesis of an oxetene was that of the 2-ethoxy-4,4-di(trifluoromethyl) derivative in 1965, by reacting di(trifluoromethyl) ketone with ethoxyethyne at -78 °C (Scheme 8.11). At room temperature the product undergoes ring fission to ethyl 3,3-bis(trifluo-romethyl)propenoate. 

Oxetans.—Stable oxetens are rare another example (56), this time stabilized by the pstfluoroalkyl effect , has been reported. The Paterno-Buchi reaction cannot be used for the synthesis of 2,2-dialkyl-oxetans from aliphatic ketones. A convenient, one-step conversion of such ketones into oxetans involves use of the sulphoximide (57) and proceeds via ring-expansion of an epoxide intermediate. Unusually high asymmetric induction has been observed in the Paterno-Buchi reaction of (-)-menthyl phenylglyoxylate with tetramethylethylene. The visi-... 

The enantioselective Lewis-acid-promoted 2 -t- 2-cycloaddition of trifluoropyruvate with various alkynes produced stable oxetene derivatives for use in the synthesis of pharmaceuticals and agrochemicals. l,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed 2- -2-cycloaddition of allenoates and trifluoromethylketones produced 2-alkyleneoxetanes in good yields and with good diastereo-selectivities dr > 20 1). A cinchona alkaloid (20) catalysed the 2- -2-cycloaddition between tV-sulfonylimines and alkyl 2,3-butadienoates to form / -configured 2,4-disubstituted azetidines in high yields and with high enantioselectivities. ... 

Recently, (15a)-type allylsilanes such as (17) have been used for the stereoselective synthesis of dihydropyrans and oxetenes (Scheme 9.18) [66, 67]. The (la)-promoted annulations of enantioenriched a-chiral allylsilanes (18) (I5a)-type and (19) (15c)-type with aldehydes proceed with high levels of chirality transfer... 

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