17.5 The Wittig and Related Reactions (formation of alkenes)

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17.5 The Wittig and Related Reactions (formation of alkenes) Main Menu 17.5 The Wittig and Related Reactions The Wittig Reaction (formation of alkenes) General Reaction: R´ and R” can be H or alkyl group. Phosphine oxide Wittig reagent (a phosphonium ylide)

Formation of Wittig Reagents General Reaction: base A phosphonium salt Ph: phenyl The alkyl halides need to have at least one H. Example: Potassium tert-butoxide

Mechanism of Wittig Reaction oxaphosphetane betaine

Examples of Wittig Reaction major minor Wittig reagents favor the Z (cis) isomer.

Reactions of Aldehydes and Ketones with Horner-Emmons Reagent Horner-Emmons reaction (general reaction): R = Et (most common) Phosphate diester Horner-Emmons reagent

Formation of Horner-Emmons Reagent Arbuzov (Perkow) reaction: base R = alkyl, acyl or R’OC(O)- Stabilized carboanion

Mechanism of Horner-Emmons Reaction oxaphosphetane betaine Water insoluble Water soluble

Examples of Horner-Emmons Reaction > 99% Horner-Emmons reagents favor the E (trans) isomer.

Learning Check 1. What could be the reagent for the following transformation? 2. What should be the product from the following reaction?

Learning Check Main Menu 3. What could be the product for the following reaction?