21613-45-6Relevant academic research and scientific papers
Synthesis via Isoxazolines, 4. - Base-initiated Ring Opening of 2-Isoxazolines; Synthesis of α-Enoximes and -Enones from Alkenes
Grund, Hartmut,Jaeger, Volker
, p. 80 - 100 (2007/10/02)
The 2-Isoxazolines 2a-e and 5 undergo ring cleavage on treatment with lithium diisopropylamide (LDA) at -78 --> 0 deg C to afford sterically homogeneous α-enoximes 3a-e and 6. 1H- and 13C-NMR data establish that these compounds have retained the C=N-configuration of the starting isoxazoline.Subsequent deoximation by acidic TiCl3 solution in DMF yields the α-enones 4a-e and the tetrahydropyran 7, respectively.This constitutes a new, regioselective sequence (1 --> 4) for the acylation of alkenes, which avoids cationic intermediates.Studies to determine the mechanistic course and the scope of the ring cleavage reaction show that endo and/or exo anions are formed first, depending on the substitution pattern.The former may isomerize ( -78 deg C) to produce enoximates; both offer the possibility to prepare new 4- or 3α-substituted isoxazolines by the reaction with electrophiles as demonstrated by two examples (2f, 2h).
