C. M. Gober et al. / Tetrahedron Letters 53 (2012) 4536–4537
4537
Table 1
tert-Butylcarbonimidic dichloride (2c)
Synthesis of isonitrile dichlorides using sulfuryl chloride
1H NMR d 1.39 (s, 9 H); 13C NMR d 116.4, 59.9, 28.5; IR 1648;
EIMS m/z 153 (M+), 155 (M++2), 157 (M++4); 138, 140, 142 (loss
of CH3); 57 (base peak).
Isonitrile
Isonitrile dichlorides (% Yield)
Lit. reference
1a R = n-butyl
1b R = cyclohexyl
1c R = t-butyl
1d R = o-tolyl
1e R = TsCH2
2a (80)
2b (99)
2c (90)
2d (98)
2e (97)
2f (98)
8
9
9b
9a,b,10
11
(2-Methylphenyl)carbonimidic dichloride (2d)
1f R = CH2CO2Et
1H NMR d 7.25–7.17 (m, 3 H), 7.13 (td, 1 H, J = 7.5, 1.4 Hz), 6.82
(dd, 1 H, J = 7.8, 1.3 Hz), 2.17 (s, 3H); 13C NMR d 144.5, 130.6, 128.4,
126.4, 125.9, 118.9, 17.6; IR (cmꢀ1) 1647; CIMS (electron impact,
m/z): 188 (MH+), 190 (MH++2), 192 (MH++4).
decomposition, but NMR samples deteriorated appreciably upon
standing at rt after 1–2 d.
When dichloride 2c was analyzed using CIMS, no parent ion
could be detected, likely because of the facile fragmentation of pro-
tonated 2c shown in Eq. 2. However the EIMS spectrum of 2c re-
vealed the expected M, M+2 and M+4 pattern of parent ions, as
{[(4-Methylphenyl)sulfonyl]methyl}carbonimidic dichloride
(2e)
1H NMR d 7.83 (d, 1 H, J = 8.3 Hz), 7.39 (d, 1 H, J = 8.0 Hz), 4.79
(s, 2 H), 2.47 (s, 3 H); 13C NMR d 145.7, 134.0, 129.9, 129.0, 128.8,
73.9, 21.7; IR 1650; CIMS m/z 266 (MH+), 268 (MH++2), 270
(MH++4).
well characteristic fragment ions resulting from both
and inductive cleavage pathways.
a-cleavage
H
CIMS
N
CCl2
HN
CCl2
+
ð2Þ
Ethyl [(dichloromethylidene)amino]acetate (2f)
2c (protonated)
1H NMR d 4.29 (s, 2 H), 4.26 (q, 2 H, J = 7.2 Hz), 1.30 (t, 3 H,
J = 7.2 Hz); 13C NMR d 167.3, 129.9, 61.7, 55.6, 44.1, 14.1; IR
1662; CIMS m/z 184 (MH+), 186 (MH++2), 188 (MH++4).
Data in Table 1 confirm that the reaction is compatible with other
functionality, including carboxylic esters. Moreover, no aromatic
chlorination products were detected. In a competition experiment
between cyclohexylisonitrile and 1-decene, dichloride 2b was
formed exclusively (94%) and 1-decene was returned unchanged,
indicating high selectivity for chlorine addition to the isonitrile in
the presence of an alkene. Furthermore, isonitriles 1d–1f selectively
underwent addition in preference to substitution, even in the pres-
ence of activated methyl and methylene groups (e.g., CH3–Ar in 1d;
–SO2CH2– in 1e; –CH2CO2Et in 1f).
Acknowledgments
Funding for H.V.L. was provided by the NIH (GM 008500 train-
ing Grant). Support of the Cornell NMR Facility has been provided
by NSF (CHE 7904825; PGM 8018643) and NIH (RR02002).
Supplementary data
Experimental
Supplementary data (Full 1H NMR, 13C NMR, infrared and mass
spectra are provided for all compounds reported in the Table) asso-
ciated with this article can be found, in the online version, at
Representative procedure for the chlorination of isonitriles
using SO2Cl2
A
magnetically-stirred CHCl3 solution of isonitrile (0.7–
References and notes
1.0 mmol) under N2 in an oven-dried 25 mL RBF was cooled in a
dry ice-CHCl3 bath to ꢀ45 °C. A solution of freshly distilled SO2Cl2
(1 equiv) in CHCl3 (1 M) was added dropwise via microsyringe over
10 min and the resulting solution was stirred for 10 min, then al-
lowed to warm to rt. The desired product was obtained by concen-
trating the solution on a rotary evaporator and briefly exposing the
residual oil to a vacuum line (0.1–0.25 torr, 1–2 min) to remove
last traces of solvent. The product carbonimidic dichlorides were
characterized without further purification.
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