ANOMALOUS EPOXIDE FORMATION UPON WITTIG OLEFINATION WITH 1-IODOETHYL TRIPHENYLPHOSPHONIUM YLIDE

Reaction of iodo Wittig ylide 1 with aldehyde 2 affords moderate yield s of cis epoxides 6a and 7a, in addition to the expected olefin 3. A m echanism is proposed to account for both the high Z selectivity and th e modest yield of olefin observed with this reagent. Recently we repor ted the total synthesis of the immuno-suppressive/antitumor agent (-)- discodermolide (4).(1) A key component of our convergent synthetic str ategy was the use of vinyl iodide 3 as the C(9)-C(14) subtarget (Schem e 1). Iodide 3 was conveniently prepared from aldehyde 2 employing the Zhao protocol for 2-iodo-2-alkene construction (Scheme 2).(2) Accordi ngly, treatment of aldehyde 2 with ylide 1 afforded 3 as a 6:1 (Z/E) m ixture of olefins in 41% yield.(1)