Lecture 5 Carbene reactions

Question 1

Singlet cycloaddition to alkene

Answer 1

Concerted
stereospecific
trans ->trans
cis->cis

Question 2

Triplet cycloaddition to alkene

Answer 2

diradical

non stereospecific due to spin flip - bond rotation occurs in between

Question 3

cycloaddition to 1,3 diene

Answer 3

butadiene +CR2
delta
vinyl cyclopropare produced -> delta -> alkyl shiftrearrange

Question 4

What does CCl2 add easily to?

Answer 4

electron rich aromatics
eg toulene - benzene w/cho
pyridine (5m)-> 6 member hetro aromatic!!

Question 5

cycloaddition to arenes

Answer 5

C(H)(CO2Et)
N2-CHR from

arene 6 -> extra H cycles round co2Et stays

Question 6

Insertion into XH bonds

Answer 6

R2C + HX -> R2C(X)(H)

N2-> RhCR2-> (X)(H)CR2

Question 7

Insertion into CH - Triplet

Answer 7

CR2 + HCR3 -> CHR2 rad and CR3 rad

combine HR2C-CR3

Question 8

Insertion into CH - Singlet

Answer 8

concerted 
triangular transition state
R2C + HCR3
HR2C-CR3
stereochem retained

Question 9

Reaction with nucleophiles aka RXR

Answer 9

CR2 +XRX -> YLID
R2C(neg)-(pos)XR2

migration will then occur- 1,2 or 2,3
group best at stabilising positive charge will migrate

Question 10

1,3 dipole

Answer 10

dipole formed when n2 taken away -> da

C=X-CR2-N2

Question 11

Rearrangements

Answer 11

if carbene doesnt react with anything else
they rearrange
migration H>aryl>alkyl

Question 12

Wolff rearrangement

Answer 12

C(H)(COR) -> R-C=·=O

open to Nu attack at middle carbon (one right next to O)