Handbook of Functionalized Organometallics Applications in S

Pent I
O
O
Pent I
CO 2Et
O
Br
Pent
(Nphyl) 2CuLi
-78 ºC, 1 h
9.2 Preparation of Functionalized Organocopper Reagents
CO 2Et
Pent Cu(Nphyl)Li
O
O
Cu(Nphyl)Li
Br
Br
Br
44 45 46: 76%
O
COPent
O
Pent
Pent Cu(Nphyl)Li
Cl
I
N
O
Cl
Pent
CO 2Et
41 42
O
43: 81%
(Nphyl) 2CuLi
-78 ºC, 0.5 h
(Nphyl) 2CuLi
-100 ºC, 5 min
c-HexCOCl
O
O
Pent
47 48 49: 81%
Scheme 9.12 Preparation of functionalized alkenylcopper
derivative via a halogen/copper-exchange.
ing copper species 50 by addition of CuCN and MeLi. Schaumann and coworkers
describe a conjugate diastereoselective addition of phenyldimethylsilyl cuprate 50
to a,b-unsaturated lactones. The benzyloxymethyl substituent at C-6 directs the
attack of the silyl-nucleophile on the enone system selectively to the opposite site,
giving only the trans product 51 in 87% yield. Unmasking the latent hydroxy
function by treatment of the silyl derivative with mercuric acetate and peracetic
acid with retention of configuration, is leading to the lactone 52 that provides the
key intermediate in the synthesis of the lactone unit of compactin (Scheme 9.13)
[24].
Dieter and Nice have studied the reaction of a-amino cuprates such as 53a,b
prepared from carbamates via sequential deprotonation and treatment with
CuCN´2LiCl followed by reaction with propargylic reagents like epoxides and
mesylates affording aminoallenes such as 54a,b via an S N2¢ substitution process.
The allene 54b can be easily converted to the corresponding pyrrolidine 55 via
Boc-deprotection and treatment with AgNO 3. The reaction can be performed with
catalytic amounts of silver salt and is very reliable. It tolerates a wide range of substituents.
Unfortunately, moderate diastereoselectivities are often observed
(Scheme 9.14) [25].
Yamamoto et al. have described an asymmetric conjugate addition of copper
azaenolates such as 56 derived from an acetone imine of optically active erythro-2-
O
Cl
387
O
N