The reaction of stable phosphoranes with phthalic anhydride - a case of cis-trans isomerism.

On the mechanism of Wittig reactions with cyclic anhydrides. II.

“…The higher energy, but also more highly organized, transition state leading to enol-lactones explains adequately the regio-and stereoselectivity observed in reactions of stabilized ylides with cyclic anhydrides. It is in agreement with Chopard's explanation of high E-selectivity observed in the reactions of stabilized ylides with phthalic anhydrides (12) and our justification of regioselectivity observed in 2-methoxymaleic (3), 2-methoxysuccinic (2), and 3-methoxy-and 3-nitrophthalic anhydrides (1).…”

“…The mechanisms of reactions of stabilized ylides with cyclic anhydrides have been the subject of much speculation and several reaction pathways have been proposed (1)(2)(3)(4)(11)(12)(13)(14). The data obtained in this study indicate that the formation of acyclic intermediate(s) is a reversible process, with an apparently quite low energy transition state.…”

“…General procedures for low-temperature condensations and for reactions canied out under anhydrous conditions are described in previous papers (12,13). 12 mmol) suspended in 10 mL of CHCI, was cooled to -5'C.…”

Mechanism of Wittig reaction with cyclic anhydrides

“…erentially the E product (16). The fact that E selectivity was shown to increase with the electron-donating capacity of the I Author to whom correspondence may be addressed.…”

“…The enol-lactones produced in these reactions showed a surprisingly high stereoselectivity in favour of E geometry (16). 1 To account for this selectivity, Chopard suggested a cyclic According to this scheme, the electron-rich system intertransition state with the COX group of the ylide in the plane acts with the electron-deficient aromatic ring to give pref-1 parallel to the phenyl ring of phthalic anhydride, Fig.…”