Sequestered alkyllithiums: why phenyllithium alone is suitable for betaine-ylide generation.
The key step in the trans-selective modification of the Wittig reaction is the alpha-lithiation of the lithium bromide coordinated ylide-aldehyde adduct (the so-called "P-betaine"). Only phenyllithium effects this deprotonation rapidly and cleanly. Alkyllithiums (in particular, butyl-, sec-butyl-, and tert-butyllithium) react only sluggishly and incompletely, being tied up in very stable mixed aggregates with the lithium alkoxide part of the betaines.
Wang
Qian
Q
Institut de Chimie Organique, Université, BCh 1015 Lausanne, Switzerland.
Deredas
Dariusz
D
Huynh
Cyril
C
Schlosser
Manfred
M