Chemistry Reference
In-Depth Information
O
O
O
RNH
2
Me
R
Ph
H
S
Ph
H
H
Ph
Ph
H
H
787
788
(85 %)
793
(40-65 %)
HCl,H
2
O
O
O
LDA
Me
Me
Ph
Li
S
Ph
H
S
787
792
O
route A
route B
LDA
Me
SS
Me
Ph
NH
2
786
YH
H
2
N
route C
(CH
2
)
n
789
O
O
n = 2, 3
YH = NH
2
, OH
R = alkyl
HY
n
(H
2
C)
(CH
2
)
n
YH
+
Y
(CH
2
)
n
NH
H
H
791
(75-100 %)
790
(40-80 %)
By carrying out the reaction under basic conditions (LDA), the intermediate 787 is
deprotonated immediately after its formation, giving the corresponding lithium
salt 792 in quantitative yield. The latter is relatively stable toward nucleophilic
substitution at ambient temperature and will not react further to give dibenzylurea
(route B). Unfortunately, this method cannot be employed with amino acids due to
the requirement for LDA, which would racemize any stereogenic center.
Typical procedure. S-Methyl N-alkylthiocarbamates. S-Methyl N-benzylthiocarbamate 787
[577]:
To a solution of benzylamine (0.93 g, 0.87 mmol) and diisopropylamine
(0.89 g, 8.8 mmol) in THF (20 mL) at
78
C under nitrogen was added a solution
of n-BuLi (1.6 m, 10.9 mL, 17.5 mmol) in hexane. Following the addition, the so-
lution was stirred at
78
C for 0.5 h, and then a solution of DMDTC (1.07 g, 8.8
mmol) was added. The resulting mixture was allowed to react at room temperature
for 20 h. Thereafter, the reaction was quenched by pouring the mixture into ice/
dilute aq. HCl. The crude solid obtained was dissolved in EtOAc, and this solu-
tion was washed with aqueous Na
2
CO
3
solution and brine, dried over anhydrous
MgSO
4
, and concentrated under reduced pressure. The residue was recrystallized
from hexane to provide S-methyl N-benzylthiocarbamate 787 as colorless crystals
(0.95 g, 62%).
