56
3 Theoretical Study of Rh-Catalyzed …
Fig. 3.43 Free energy profiles for Rh(III)-catalyzed intramolecular C–H bond activation and
alkenylation of O-Me N-hydroxybenzamides and alkyne-tethered cyclohexadienone. The values
are the relative free energies given in kcal/mol calculated at the M06/6-311+G(d,p)/SDD//M06/631G(d)/LANL2DZ level of theory in DMF
2.5 mol % [Cp*RhCl 2 ] 2
+
O
N
H
Ac
25 C, 16h
1.2 eq. AcOH
0.25 eq. CsOAc
DCM, 60C, 16h
32 - 83 % yield
47 - 90 % yield
R 1
R 2
MeOH
OH
R 1
R 2
HN Ac
O
R 1
R 2
Scheme 3.44 Rhodium(III)-catalyzed C–H alkenylation reaction of N-phenoxyacetamides with
alkynes
into C(aryl)–Rh bond via transition state 3-238ts to afford an amido Rh(III) intermediate 3-239. Two sequential protonations yield ortho-hydroxyphenyl enamide 3-240
(Fig. 3.45).
As shown in Fig. 3.46, when acetate acid was used as an additive, the protonation
of Rh–nitrene complex 3-237 provides a hydrogen bond complex, which restricts
the insertion of nitrene. Alternatively, a C(vinyl)-O(phenoxy) reductive elimination