Exam 2 - Wittig Reaction, HWE Reaction, and Ylides Flashcards
In the ___ ___, you add phosphonate and NaOCH3 (base) to a ketone/aldehyde in order to create an attached E alkene.
HWE Reaction
Strong bases for the conversion of phosphonium salt to an ylide include:
NaH, NaNH2, nBuLi, R-Li
You can make a phosphonium ylide by reacting ___ with ___, to make a phosphonium salt. Then, add a strong base such as ___ or ___ to the phosphonium salt, in order to make the phosphonium ylide.
triphenylphosphine reacts with CH3-X (Where X = I,Br,Cl, etc.) to make the phosphonium salt. Then, add nBuLi or R-Li (strong base) to convert the phosphonium salt to a phosphonium ylide.
In the HWE Reaction, you add phosphonate and NaOCH3 (base) to a ketone/aldehyde in order to create a(n) ___ ___ ___.
attached E alkene
Stabilized ylides will produce ___ alkenes.
E alkenes (trans)
*Note: You have to make the ___ for the HWE Reaction!
phosphonate
*Note: If the Wittig reagent is an alkane larger than CH2, then the stereochemistry of the alkene will usually be ___.
Z
In the HWE Reaction, you add ___ and ___ to a ketone/aldehyde in order to create an attached E alkene.
phosphonate and NaOCH3 (base)
Stabilized ylide -> Ylide stabilized by ___ ___ ___.
nextdoor carbonyl group
*___ your carbons to make sure you don’t lose any along the way!
Count Carbons
In the Wittig Reaction, you react with a ___ ___ to convert a ketone/aldehyde to an alkene.
phosphonium ylide
___ ylides will produce E alkenes (trans).
Stabilized ylides
You need to make the phosphonate by adding either ___ or ___ to ___.
Add Br-Ester or Br-ketone to phosphite [P(OCH3)3] to make the phosphonate.
*Note: You have to make the ___ ___ for the Wittig Reaction!
phosphonium ylide
The E alkene may be ___ ___, but the intermediate can only change to E if the ylide is stabilized!
thermodynamically favored
In the ___ ___, you react with a phosphonium ylide to convert a ketone/aldehyde to an alkene.
Wittig Reaction
___ ___ -> Ylide stabilized by nextdoor carbonyl group.
stabilized ylide
*Note: If the Wittig reagent is a(n) ___ larger than ___, then the stereochemistry of the alkene will usually be Z.
alkane larger than CH2
___ ylides will produce Z alkenes (cis).
Unstabilized ylides
A(n) ___ is when there are opposing charges on neighboring atoms, where one C does NOT have a full octet.
ylide
You need to make a phosphonium salt by adding ___ and/or ___ ___ to triphenylphosphine. If you add a tertiary halide, you will do an E2 reaction instead.
primary and/or secondary halides
In the Wittig Reaction, you react with a phosphonium ylide to convert a ketone/aldehyde to a(n) ___.
alkene
Unstabilized ylides will produce ___ alkenes.
Z alkenes (cis)
