Chemistry Reference
In-Depth Information
and concentrated. The residue was purified by means of column chromatography
on silica gel (eluent: benzene) to give the cyclic carbamate 606 (R
1
H, R
2
¼
¼
H,
R
3
H, R
4
Ts) in 94% yield; mp 145.0-145.5
C.
¼
¼
O
O
O
O
n
-C
8
H
17
n
-C
6
H
11
CH
2
OO
HH
H
H
607
608
609
LP of carpenter
bee
LP of black-tailed
deer
LP of Japanese
beetle
O
n
-C
8
H
17
n
-C
11
H
23
O
O
O
610
611
LP of Oriental
hornet
LP of rove beetle
Enantiomerically pure lactonic pheromones 607-611, of the carpenter bee, black-
tailed deer, Japanese beetle, rove beetle, and Oriental hornet, respectively, have
been synthesized from racemic cyano alcohols of type 612. The key to the success
of the overall approach is the facile separation of diastereomeric carbamates de-
rived from cyano alcohols of type 612 by automated multigram LC. The chosen
approach also facilitates the assignment of absolute configurations to the lactone
enantiomers and their precursors. In the case of 607, direct determination of
enantiomeric purity and absolute configuration is also possible using the chiral
solvating agent 2,2,2-trifluoro-1-(9-anthryl)ethanol [439].
Typical procedure. 1-Methyl-4-cyanobutyl N-[1-(1-naphthyl)ethyl]carbamates 614 (R
¼
Me, n
4) [439]. Procedure A: A stirred solution of 5-cyanopentan-2-ol (8.0 g,
70.8 mmol), (R)-(
¼
)-1-(1-naphthyl)ethyl isocyanate (13.9 g, 70.8 mmol), dry ben-
zene (150 mL), and two drops of dimethylethanolamine catalyst was heated at
reflux under N
2
for 24 h. The solvent was then removed in vacuo, and the crude
diastereomeric carbamates were completely separated by chromatography (on
acidic alumina, eluting with CHCl
3
/hexane, 2:1) using an automated preparative
LC system. A total of 8.9 g (81%) of the high R
f
(R,R) diastereomer was collected
as a yellow viscous oil.
(Z)-1-(2-Cyanoethyl)-3-nonene N-[1-(1-naphthyl)ethyl]carbamates
C
614
(R
¼
3-
nonene, n
4) [439]. Procedure B: To a stirred solution of phosgene (5.8 g, 58.6
mmol) (for a safe source, see Chapter 7) in dry toluene (75 mL) at
¼
5
C under N
2
,
