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Topics in Current Chemistry (2020) 378:16
carbonate and subsequent elimination of tert-butoxide and CO 2 giving an allylic
ammonium electrophile. Meanwhile, N-coordination of Ag(I) to the benzoxazole
facilitates deprotonation by the tert-butoxide released from the MBH carbonate, giving the active nucleophile. Thereafter, S N 2′-type addition of the enamine to the electrophile followed by elimination of triethylamine gives the product and returns each
catalyst. This example is distinct from the modes of catalysis previously discussed in
O
N
R 1
OBoc
COOR 3
R 2
CO 2 R 3
R 2
R 1
N
O
X
X
AgOAc (10 mol%)
DABCO (10 mol%)
PhMe, rt, 14 h
19 Examples all >15:1 d.r.
CO 2 Me
N
O
O 2 N
CO 2 Me
N
O
O 2 N
CO 2 Me
N
O
O 2 N
CO 2 Me
N
O
N
CO 2 Me
n Pr
N
O
CO 2 Me
Cl
N
O
%
9
9
%
7
9
%
2
9
%
0
1
%
2
9
%
5
6
Br
O 2 N
Cl
Cl
Cl
O 2 N
O 2 N
R 3 N
Ar
CO 2 Me
OBoc
Ar
CO 2 Me
NR 3
Ar
CO 2 Me
NR 3
O
N
O 2 N
Ar
CO 2 Me
O
N
O 2 N
Ag
O
N
O 2 N
Ag
O
N
O 2 N
Ag
CO 2 , t BuO
t BuO –
t BuOH
Selected Examples:
Proposed Mechanism:
Scheme 15 Diastereoselective addition of benzoxazoles to carbonates by Rios
Reprinted from the journal
113