76
3 Theoretical Study of Rh-Catalyzed …
3-396ts
3-397ts
3-398ts
3-399ts
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
G = 25.4 kcal/mol
G = 24.3 kcal/mol
G = 23.7 kcal/mol
G = 25.5 kcal/mol
3-400ts
3-401ts
3-402ts
3-403ts
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
G = 18.0 kcal/mol
G = 20.1 kcal/mol
G = 21.4 kcal/mol
G = 22.4 kcal/mol
O
O
O
O
Fig. 3.73 The site-selectivity for Rh(III)-catalyzed redox-neutral C–H bond activation and annulation of nicotinamide and its N-oxide derivative with alkynes. The values are the relative free
energies given in kcal/mol calculated at the M06/6-311+G(d,p)/SDD//M06/6-31G(d)/LANL2DZ
level of theory in methanol
2.5 mol % [Cp*RhCl 2 ] 2
2 eq. NaOAc
PhBr, 130 C, 2 h
48 - 85 % yield
+
R
4
R
5
N
N
O
R
2
R
3
R
1
R
1
N
O
R
3
H 2 N
R
2
R
4
R
5
Scheme 3.74 Rh(III)-catalyzed redox-neutral C–H bond activation and annulation reaction of
pyrazolones with alkynes
the Rh–C bond rather than the Rh–N bond occurs via transition state 3-410ts with
an energy barrier of 10.4 kcal/mol leading to the extension of rhodacycle in 3-411.
The following reductive elimination takes place via a four-membered ring-type vinyl
migration transition state 3-412ts with a barrier of 21.5 kcal/mol to give a zwitterionic
Rh(I) intermediate 3-413. Then an N–N bond cleavage occurs via oxidative addition
transition state 3-414ts involves a free energy barrier of 15.7 kcal/mol to give the
Rh(III)-nitrene complex 3-415. After the N–N bond cleavage, the desired indole
product 3-416 is obtained and the active catalyst 3-404 is regenerated through two
steps of protonolysis of the N atom by two acetic acids.
In another example, Lin and co-workers [177] reported a theoretical study for the
Rh(III)-catalyzed C–H activation and annulation reaction of acetylhydrazinyl arenes
with alkynes to prepare indoles, which is developed by Glorius and co-workers
[178] in 2013. In this reaction, acetylhydrazinyl group is considered as the internal
oxidizing directing group (Scheme 3.76).
3 Theoretical Study of Rh-Catalyzed …
3-396ts
3-397ts
3-398ts
3-399ts
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
G = 25.4 kcal/mol
G = 24.3 kcal/mol
G = 23.7 kcal/mol
G = 25.5 kcal/mol
3-400ts
3-401ts
3-402ts
3-403ts
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
N
N
O
PivO
Rh
O
Me
O
H
N
N
O
PivO
Rh
Me
Me
G = 18.0 kcal/mol
G = 20.1 kcal/mol
G = 21.4 kcal/mol
G = 22.4 kcal/mol
O
O
O
O
Fig. 3.73 The site-selectivity for Rh(III)-catalyzed redox-neutral C–H bond activation and annulation of nicotinamide and its N-oxide derivative with alkynes. The values are the relative free
energies given in kcal/mol calculated at the M06/6-311+G(d,p)/SDD//M06/6-31G(d)/LANL2DZ
level of theory in methanol
2.5 mol % [Cp*RhCl 2 ] 2
2 eq. NaOAc
PhBr, 130 C, 2 h
48 - 85 % yield
+
R
4
R
5
N
N
O
R
2
R
3
R
1
R
1
N
O
R
3
H 2 N
R
2
R
4
R
5
Scheme 3.74 Rh(III)-catalyzed redox-neutral C–H bond activation and annulation reaction of
pyrazolones with alkynes
the Rh–C bond rather than the Rh–N bond occurs via transition state 3-410ts with
an energy barrier of 10.4 kcal/mol leading to the extension of rhodacycle in 3-411.
The following reductive elimination takes place via a four-membered ring-type vinyl
migration transition state 3-412ts with a barrier of 21.5 kcal/mol to give a zwitterionic
Rh(I) intermediate 3-413. Then an N–N bond cleavage occurs via oxidative addition
transition state 3-414ts involves a free energy barrier of 15.7 kcal/mol to give the
Rh(III)-nitrene complex 3-415. After the N–N bond cleavage, the desired indole
product 3-416 is obtained and the active catalyst 3-404 is regenerated through two
steps of protonolysis of the N atom by two acetic acids.
In another example, Lin and co-workers [177] reported a theoretical study for the
Rh(III)-catalyzed C–H activation and annulation reaction of acetylhydrazinyl arenes
with alkynes to prepare indoles, which is developed by Glorius and co-workers
[178] in 2013. In this reaction, acetylhydrazinyl group is considered as the internal
oxidizing directing group (Scheme 3.76).