Phản ứng chuyển vị б (Sigmatropic rearrangement) Nhóm thực hiện: Nhóm 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 major categories : I Generalization : II Suprafacial and Antarafacial processes III.[1,3] Sigmatropic Rearrangements [1,3] Sigmatropic Rearrangements: H migration [1,3] Sigmatropic Rearrangements: C migration IV [1,5] Sigmatropic Rearrangements [1,5] Sigmatropic Rearrangements: H migration [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 [1,3] 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 [1,3] Sigmatropic Rearrangements: H migration [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 - It has been observed that in a [1,3] thermal suprafacial process, symmetry is conserved only if the migrating carbon has opposite lobes 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' [1,5] 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' [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 [1,5] Sigmatropic Rearrangements : C migration V [3,3] Sigmatropic Rearrangements 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 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 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 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 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)  .. .Nhóm thực hiện: Nhóm Nguyễn Thị Kiều Oanh Nguyễn Xuân Phong Nguyễn Thị Thắm Trần Thị Ngân Thoa Nguyễn Thị... 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 major categories : I Generalization : II... 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