HỮU cơ NC THUYẾT TRÌNH NHÓM

Phản ứng chuyển vị б
(Sigmatropic rearrangement)


Nhóm thực hiện: Nhóm 3
Nguyễn Thị Kiều Oanh
Nguyễn Xuân Phong
Nguyễn Thị Thắm
Trần Thị Ngân Thoa
Nguyễn Thị Kim Thoa
Phạm Quang Thống
Phan Vũ Thuyền
Nguyễn Đinh Ngọc Trâm
Lương Văn Tri
Nguyễn Thị Mai Trinh
Nguyễn Hữu Trọng


Sigmatropic
Phản ứngRearrangements
chuyển vị б
5 major categories :
I. Generalization :
II. Suprafacial and Antarafacial processes.
III.[1,3] Sigmatropic Rearrangements
1. [1,3] Sigmatropic Rearrangements: H migration
2. [1,3] Sigmatropic Rearrangements: C migration
IV. [1,5] Sigmatropic Rearrangements
1. [1,5] Sigmatropic Rearrangements: H migration
2. [1,5] Sigmatropic Rearrangements: C migration

V. [3,3] Sigmatropic Rearrangements


Phản ứng
chuyển vị б
Sigmatropic
Rearrangements
I. Generalization :

• Migration of a s-bond across a conjugated p-system
• [i,j] shift when the s-bond migrates across i atoms of one
system and j of another


II. Suprafacial/Antarafacial
- Suprafacial migration: Group moves across same face
- Antarafacial migration: Group moves from one face to the other


III. [1,3] Sigmatropic Rearrangements
1. [1,3] Sigmatropic Rearrangements: H migration
- Suprafacial [1,3] hydrogen shift under thermal condition is
forbidden. Antarafacial [1,3] hydrogen shift is allowed only by
the principles of orbital symmetry. The transition state is a highly
contorted species and the reaction is forbidden because of the
steric inhibition involved in such a process


1. [1,3] Sigmatropic Rearrangements: H migration

1. [1,3] Sigmatropic Rearrangements: H migration

- Photochemical HOMO ( Ψ3) of this radical has same sign on the
terminal lobes (m symmetry), which permits suprafacial [1,3]
hydrogen shift


III. [1,3] Sigmatropic Rearrangements
FMO Analysis of [1,3] Sigmatropic Rearrangements of Alkyl
Group
2.

- It has been observed that in a [1,3] thermal suprafacial
process, symmetry is conserved only if the migrating
carbon has opposite lobes


2. FMO Analysis of [1,3] Sigmatropic Rearrangements of Alkyl Group

- However, the [1,3] thermal suprafacial process that involves the same lobe gives
the product with retention of configuration in the migrating group, but the process is
not symmetry allowed. On the other hand, symmetryallowed [1,3] thermal
antarafacial process with retention is geometrically forbidden and antarafacial
process with inversion is symmetry forbidden


IV. [1,5] Sigmatropic Rearrangements
X

R

X

+

X
R'

R

R'

R

R'

1. [1,5] Sigmatropic Rearrangements : H migration
- The [1,5] sigmatropic shift of hydrogen or deuterium atom occurs via a
suprafacial pathway under thermal conditions
- The ground state electronic configuration of pentadienyl radical is Ψ12
Ψ 22 Ψ31
- [1,5] suprafacial migration will be a thermally allowed process
- Under photochemical conditions [1,5] suprafacial migration is no
longer possible and the shift has to be an antarafacial process


IV. [1,5] Sigmatropic Rearrangements

IV. [1,5] Sigmatropic Rearrangements
Example:


IV. [1,5] Sigmatropic Rearrangements
X

R

X

+

X
R'

R

R'

R

R'

2. [1,5] Sigmatropic Rearrangements : C migration
During [1,5] thermal suprafacial process, symmetry can be
conserved only if the migrating carbon involves the same lobe. In
other words, if the migrating carbon atom was originally bonded
via its positive lobe, it will have to use its positive lobe to form
the new C-C bond. The entire process results in the retention of

configuration in the migrating group. However, if migrating
carbon uses the opposite lobe, it may give the product with
inversion of configuration, but the process becomes symmetry
forbidden. On the other hand, [1,5] thermal antarafacial process
with retention is symmetry forbidden and antarafacial process
with inversion is symmetry allowed


IV. [1,5] Sigmatropic Rearrangements
2. [1,5] Sigmatropic Rearrangements : C migration


V. [3,3] Sigmatropic Rearrangements
1. The Cope Rearrangement
[3,3] sigmatropic
of is
1,5--InThe
thethermal
Cope rearrangement,
therearrangement
migrating group
an
dienes
is called
the Cope
rearrangement
allyl
radical.
An analysis
of the

symmetry of the orbitals
involved shows that [3,3] sigmatropic rearrangements are
thermally allowed and photochemically forbidden


V. [3,3] Sigmatropic Rearrangements
1. The Cope Rearrangement


- Stereochemistry of the Cope Rearrangement: Boat
versus Chair Transition State
- In [3,3] sigmatropic shifts, a chair-like transition state is
energetically preferred to aboat-like structure. Rearrangement of
the meso diene through such a transition state then would give
the cis - trans isomer


V. [3,3] Sigmatropic Rearrangements
1. The Cope Rearrangement
- Stereochemistry of the Cope Rearrangement: Boat versus
Chair Transition State
- The case of the rearrangement of the racemic mixture the transtrans
isomer is the major product


V. [3,3] Sigmatropic Rearrangements
2. The Claisen Rearrangement
- The Claisen rearrangement is a [3,3] sigmatropic
rearrangement in which an allyl vinyl ether is converted
thermally to an unsaturated carbonyl compound

The Claisen rearrangement of allyl vinyl ether


V. [3,3] Sigmatropic Rearrangements
2. The Claisen Rearrangement
The aromatic Claisen rearrangement involves the thermal
transformation of a prop-2-enyl phenyl ether (1) into a
2-(prop-2-enyl)-cyclohexa-3,5-dienone (2).