Lecture 3 Flashcards
1
Q
What metals are typically used as catalysts in coupling reactions?
A
- Dominated by Pd(II)/Pd(0) systems
2
Q
What are the requirements for R1 in coupling reactions? (R1X)
A
- no beta hydrogens
- to prevent elimination
3
Q
What is X in a coupling reaction?
A
- halide or trifoliate
Order of reactivity:
I > OTf > Br > Cl
4
Q
What are the requirements for R2 in coupling reactions?
A
can be almost anything due to fast third step
5
Q
What are the requirements for M in coupling reactions?
A
can be a range of compounds
6
Q
What are examples of Pd(II) catalysts?
A
- reduced in situ and more stable than Pd(0) complexes
- PdCl2 (polymer, insoluable in many solvents)
- (RCN)2PdCl2 (R= Ph, Me more soluble)
- (PPh3)2Pd(Cl)2 which is air stable and easily prepared from PdCl2
7
Q
What are examples of Pd(0) catalysts?
A
- Pd(PPh3)4
- Pd2(dba)3
8
Q
Negishi reaction
A
- Zinc reagents
R-I + IZn-R’
9
Q
Stille reaction
A
- tin reagents, can be used to form polymers
- Br and SnMe3 couple
cat = Pd2(dba)3. CHCl3
Pd(o-tol)3
10
Q
Suzuki reaction
A
- boron reagents e.g. RB(OH)2, RB(OR)2, RBR2
- couple to bromine reagents
- sterochemistry of vinyl group maintained
11
Q
Hiyama-Denmark
A
- Silanolates and iodine
- NaH used to deprotonate most acidic proton
- then Pd2(dba)3. CHCl3 catalyst
- Reaction occurs via Pd-O-Si species
12
Q
Kumada
A
- Gringard reagents
- not useful if any =O or basic groups are present else a reduction will occur
- 1% mol Pd2(dba)3
- 4% mol iPr-HCl to generate a carbene in situ
13
Q
Sonagashria
A
- Copper acetylide reagents
- cat Pd2(dba)3 and CuI
- Pr2NH
- copper reacts with terminal alkyne to form reactive species
14
Q
Buchwalkd- Hartwig
A
- uses amines not R2-M
- Cat Pd2(dba)3
- cat racier BUNAP
- KOBut
15
Q
Oxidative coupling advantages and challenges
A
- removes need to synthesise substrates/ halides
- more atom efficient and green
- harder to get regioselectivity and reactivity right, relies heavily on directing groups
