Phosgenation Reactions - Phosgenations - page 442

yield. Reaction of 1711 with benzylamine in the presence of Yb(OTf ) 3 (10%) in
THF/water gives the guanidine 1712 in 89% yield [1263].

Iminophosphoranes
An often used method for the preparation of carbodiimides is the aza-Wittig reac-
tion of an isocyanate with an iminophosphorane. The latter can be formed either
from an amine and triphenylphosphine dibromide or from an azide and triphe-
nylphosphine.
Syntheses of 2-anilino-3-arylsulfonylindoles from 2-arylsulfonylmethylanilines
have been accomplished by reaction of iminophosphoranes with phenyl isocyanate
[1264]. Iminophosphoranes 1714 are obtained in 82-95% yield by treating the
azides 1713 with triphenylphosphine. Carbodiimides 1716 are formed in 66-98%
yield by the aza-Wittig reaction of iminophosphoranes 1714 and phenyl isocyanate
1715. The ring closure of carbodiimides 1716 under strongly basic conditions to
afford 2-anilinoindoles 1717 proceeds in 68-83% yield.

Ph- N=C=O
1715

R 1 R R 1

R R 1 R

PPh 3

SO 2 SO 2

SO 2

CH 2 Cl 2
0-5°C, 1 h
to rt

CH 2 Cl 2
reflux
12 h

N PPh 3 N N

N 3

Ph

82-95 %
1714

1713 66-98 %

1716

NaOH
DMSO

rt, 30 min

R = H, Cl
R 1 = Ph, p-Tol

1

R SO 2 R

68-83 %
1717

Ph

H H

General procedure. N-[2-(Arylsulfonylmethyl)phenyl]-N 0 -phenylcarbodiimides 1716 [1264].
2-(Arylsulfonyl)methyl-N-(triphenylphosphoranylidene)anilines 1714 from azide:Toa
cooled (0-5 C) and stirred solution of triphenylphosphine (7.86 g, 30 mmol) in
dichloromethane (150 mL) was added a solution of azide 1713 (30 mmol) in di-
chloromethane (150 mL) under N 2 . The mixture was stirred at 0-5 C for 1 h and
then slowly warmed to room temperature. The solvent was removed in vacuo and
the residue was treated with benzene to precipitate the product, which was col-
lected by filtration and recrystallized from benzene/hexane to give a white powder
or from chloroform/hexane to give white needles of 1714.
N-[2-(Arylsulfonylmethyl)phenyl]-N 0 -phenylcarbodiimides 1716: To a stirred solution
of iminophosphorane 1714 (4.0 mmol) in dichloromethane (50 mL), phenyl iso-
cyanate 1715 (480 mg, 4.0 mmol) was added at room temperature under N 2 . After
the mixture had been refluxed for 12 h, the solvent was removed in vacuo. The
residue was washed with hexane and then recrystallized from dichloromethane/
hexane to give 1716 as white needles or as a white powder.