Wittig Reaction and Ylide Chemistry

Compare the Wittig reaction using a stabilized ylide (Ph3P=CHCO2Et) vs. an unstabilized ylide (Ph3P=CHCH3) with cyclohexanone. (a) Predict the major alkene geometry (E or Z) for each. (b) Explain the mechanistic basis for the selectivity. (c) What is the Horner-Wadsworth-Emmons modification and how does it improve E-selectivity? (d) Draw the complete mechanism for the Wittig reaction with the unstabilized ylide.