Electrophilic Attack On Alkenes Flashcards
Epimer=
Diastereomers that have the opposite configuration at only one of at least two stereogenic centres present
To change regioselectivity of electrophilic attack on alkenes (+OH)
1) BH3
2) H2O2/OH-
To make epoxide ring
mCPBA
Adding 2× OH syn (same side)
OsO4
Upjohn dihydroxylation
Ozone + alkene
-> 2× aldehyde
Alkyne -> ketone
1) Hg(OAc)2
2) H2O
Alkyne -> alcohol
1) Hg(OAc)2
2) H2O
3) NaBH4
Alkyne -> carboxylate
1) NaNH2 (->anion)
2) CO2
Alkyne -> alkene (E)
Na/NH3 + tBuOH
Alkyne -> alkene (Z)
H2 + lindlar catalyst(poisoned Pd)
For E1 need
Good leaving group
Stable cation
Not too good-a-base
E1 rule
Zaitsev’s rule
-thermodynamic preference for more substituted alkene
E2 need
Good base
Not too good-a-leabing group
E2 rule
Hofmann’s rule
Strong, sterically demanding base removes most accessible proton
E1cB need
Stabilised conjugate base
Sn1 need
Good leaving group
Stable cation
Not too good-a-nucleophile
Poor base
Effect of Ag+ on leaving group ability of halides
Makes them better l.g.’s
Sn2 needs
Good nucleophile
Poor base
Addition-elimination reaction needs
Good way to stabilise intermediate
Ketone -> imine
R’‘NH2
H+
Ketone -> oxime
Hydroxylamine (HONH2), H+
Ketone -> hydrazone
Hydrazine (H2NNH2), H+
Beckmann rearrangement conditions
H2SO4
Anomeric effect
Axial substituent favoured by lone pair- s* interaction
