Synfacts 2007(1): 0023-0023  
DOI: 10.1055/s-2006-955747
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart · New York

4-Difluoromethylene-1-Pyrrolines by Intramolecular Heck Cyclization

Contributor(s): Victor Snieckus, Todd Macklin
J. Ichikawa*, R. Nadano, N. Ito
The University of Tokyo, Japan
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Publikationsverlauf

Publikationsdatum:
15. Dezember 2006 (online)

Significance

A mechanistically interesting construction of fluoropyrrolines is reported. In the suggested mechanism, the oxidative addition product of Pd(0) insertion into the N-O bond of 2-(trifluoromethyl)allyl ketone O-pentafluorobenzoyloximes undergoes 5-endo-trig Heck cyclization (unfavorable by Baldwin’s rules) to give an α-trifluoromethyl Pd species that undergoes β-fluo­ride elimination to yield 4-difluoromethylene-1-pyrrolidines in poor to good yields. The unfavorable cyclization is overcome by the known β-arylation selectivity of trifluoromethyl groups in Heck reactions as rationalized by DFT calculations (R. J. Deeth, A. Smith, J. M. Brown J. Am. Chem. Soc. 2004, 126, 7144-7151). A stoichiometric amount of PPh3 was found to be required as the resultant F-Pd(PPh3)3 complex undergoes reductive elimination of F-PPh3, regenerating Pd(0) (V. V. Grustin Chem. Eur. J. 2002, 8, 1006-1014).