Chemistry Reference
In-Depth Information
TABLE 8E.2.
(
Continued
)
Entry
Product
Catalyst; mol %
Time (h); Temp ( ° C)
Yield (%)
ee (%)
1
O
2
; 15
48; 22
84
85
N
Me
Me
2
3a
; 5
12; 22
92
88
O
N
3
2
;5
24; 22
98
95
Me
Me
H
Cbz
4
1b
; 5
24; 22
94
97
Me
Me
H
N
Cbz
5
1b
; 5
24; 22
83
87
BnN
Me
employed to limit the number of reaction pathways; for desymmetrizations, a catalyst
may fi rst initiate on a terminal olefi n and subsequently react intramolecularly with one
of the enantiotopic olefi ns. The product shown in entry 2 of Table 8E.2 provides a rare
example of highly selective enantioselective RCM in the presence of only terminal
olefi ns (88% ee). The fi nding summarized in entry 5 of Table 8E.2 demonstrates that
substrates with 1,2-disubstituted olefi ns can participate in enantioselective RCM reac-
tions. The product obtained from the process in entry 5 was converted in two steps to
(
R
) - coniine.
Although lactams, carbamates, and tertiary amines are tolerated by Mo alkylidenes,
the presence of a secondary amine results in <2% conversion. Certain isomeric amide
substrates are also recovered intact after treatment with various Mo-based catalysts. In
one case, a stable chelate (Fig. 8E.2) of substrate-bound catalyst could be observed by
1
H - NMR spectroscopy [22] .
8E.2.4. Synthesis of Tertiary and All - Carbon Quaternary Stereogenic Centers through
Catalytic Enantioselective RCM of Enol Ethers
8E.2.4.1. The Catalytic Enantioselective Method
As discussed earlier, enantioselec-
tive RCM is often achieved through desymmetrization of an achiral substrate.
