Question

ASAP

Wittig Reaction using 9-anhraldehyde and triphosphorane

1. What is the isomer product? Why is it only produced in small amounts

2. Show the steps and mechanisms in which a ylide comes from triphosphorane.

Answer 1

The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde orketone with a triphenyl phosphonium ylide (often called a Wittig reagent) to give an alkene and triphenylphosphine oxide.^[1][2]

The Wittig reaction was discovered in 1954 by Georg Wittig, for which he was awarded the Nobel Prize in Chemistry in 1979. It is widely used in organic synthesis for the preparation of alkenes.^[3][4][5] It should not be confused with theWittig rearrangement.

Wittig reactions are most commonly used to couple aldehydes and ketones to singly substituted phosphine ylides. With unstabilised ylides this results in almost exclusively the Z-alkene product. In order to obtain the E-alkene, stabilised ylides are used or unstabilised ylides using the Schlosser modification of the Wittig reaction can be performed.

Contents

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Reaction mechanism[edit]

Classical mechanism[edit]

The steric bulk of the ylide 1 influences the stereochemical outcome of nucleophilic addition to give a predominance of thebetaine 3 (c.f. B