Exam Unit 2 Flashcards
NaBH4, workup
Aldehydes and ketones only. One reduction, except with ab unsaturated. Oxygen and “skip one” get protonated by acid component.
Will still deprotonate esters and carboxyls.
LiAlH4, workup
reduces all carbonyls. two reductions on esters and carboxyls.
Grignard formation
Add Mg, Et2OH to alkyl halide.
Grignards and Carbonyls, excess
adds once to C, once to O
grignards and carbonyls, H3O+ present
NR to carbonyl. Grignard loses MgX and is protonated.
POCl3, pyr
Dehydrates primary alcohols. E2
Acidity: Normal Alcohol
pKa 16
Acidity: Phenol
pKa10
Acidity: Carboxylic
pKa 5
Acidity
proportional to stability of conjugate base
More resonance, more acidity
Acidity: with EWG
activated rings are less acidic
Hydroboration
- BH3/THF 2. H2O2, NaOH aq.
Adds H and OH across DB, syn, non-Markovnikov
Oxymercuration
Hg(OAc)2, H2O
Adds H and OH across DB, anti, markovnikov.
Reduce ketones, aldehydes
NaBH4, H3O+ workup.
Reduce ketones, aldehydes, esters or amines
LiAlH4, H30+ work-up.
Grignard
RX+Mg gives RMGX
makes carbanion nucleophile. But incompatible with acidic protons, (pKa < 20) electrophiles.
Acidic Protons
OH, SH, NH, et cetera.
alpha, beta unsaturated carbonyl
DB adjacent to carbonyl.
With LiAlHa, only carbonyl is reduced. (Coordinates to O)
With NaBH4, single and double reductions.
peroxyacids
alkene attaches terminal oxygen, forms cyclic ether. (same stereochem as start.)
very electrophilic sources of O. mCPBA is our favorite.
mCPBA preferences
round 1: EDG > regular > EWG
round 2: if regular: constituents! the more, the merrier.
from epoxide: in acid
nucleophile chooses less hindered carbon, UNLESS TERTIARY!
sn2, except tertiary, then sn1
from epoxide, in base
nucleophile chooses less hindered carbon.
Williamson Ether Synthesis
adds R chain to OH in place of H.
NaH, RX
sn2: needs primary or secondary alcohol.
1, 2 trans diol
came from an epoxide!
1, 2 cis diol
came from OsO4!
Rules of E2
carbocation rearrangement possible
3, 2, benzylic allylic faster than primary
Zaitsev product
SOCl2
converts alcohol to halide.
Sn2, inversion
PBr3
Converts alcohol to halide. Sn2, inversion
TsCl, pyr
converts alcohols to OTs. No inversion.
TMSCl
Makes OTMS, protecting group. Remove with H2SO4
KH
Makes OH into O-
Primary alcohol from methyl halide
H20, heat
Primary alcohol from epoxide
- MeMgBr
2. H30+
Primary alcohol from ether
HI, H20
PCC
mild ox. alcohol to aldehyde or ketone
Same result as swern, CrO3 without water!
Jones
strong ox. chromic acid.
primary alcohol to carboxyl
secondary alcohol to ketone
CrO3, H20
same as Jones, KMnO4
secondary alcohols from secondary alkyl halides
h20, heat. or NaOH, DMF
secondary alcohols from aldehyde
- MeMgBr 2. H30+
secondary alcohols from alkenes
- Hg(OAc)2 2. NaBH4
secondary alcohols to carbocations
H2SO4
tertiary alcohol from ketone
- EtMgBr 2. H30 +
tertiary alcohol from alkene on tertiary carbon
- Hg(OAc)2 2. NaBH4
R-OH + Strong base
alkoxide formation! R-O-
Use for williamson ether synthesis
Cleaving ethers
add HI or HBr. Sn2
makes more substituted alcohol, less subbed alkyl halide
See: KH, DB alkyl halide
Claisen Rearrangement?
Ether from 2o alkyl iodide
MeOH, Sn1
Ether from 2o alkyl bromide
NaOMe, DMF Sn2
Ether from 2o alcohol
KH, MeI
Williams
Ether from alkene
- Hg(OAc)2, MeOH
2. NaBH4
Ether to 2o Alcohol
HBr
Epoxide from alkene
mCPBA
epoxides from OH adjacent to X
NaOH, H20
H2N-NH2, KOH, heat
Wolff Kishner!
converts ketone/aldehyde to alkane
3 ways to reduce carbonyls to alkanes
Zn, HCl (Clemmenson reduction)
H2N-NH2, KOH heat (Wolff-Kishner)
H2, Pd/C (If R group is ARYL only!!!)
See PPh3
Wittig! turns carbonyl into DB with R groups.
cis selective if R isn’t stabilized by EWG (carbonyl)
