14a
Typical Procedure for the Synthesis of Alkynes
from Enolisable Carbonyl Compounds - 4-Phenyl-but-1-yne (2c)
from 4-Phenyl-butyraldehyde (1c)
The P1-base
(1.031 g, 3.30 mmol, 2.2 equiv) was added in one lot to the vigorously
stirred mixture of 4-phenyl-butyraldehyde (0.222 g, 1.50 mmol) and
NfF (0.544 g, 1.80 mmol, 1.2 equiv) in DMF (1.5 mL) at -10 ˚C.
The reaction mixture was allowed to warm up to 20 ˚C
for the following 2 h. The three-way tap was replaced by a glass
stopper with a Teflon sleeve, and the reaction mixture was stirred
in a tightly closed flask for 20 h at ambient temperature (complete
conversion, NMR control). The reaction mixture was placed on the
top of the column and eluted with hexane. Removal of hexane in vacuum
(from 200 mbar to 15 mbar, bath at ambient temperature, no heating)
furnished pure 4-phenyl-but-1-yne (2c,
0.169 g, 87% yield) as clear colourless liquid. ¹H
NMR (270 MHz, CDCl3): δ = 1.97
(t, 4
J = 2.7
Hz, 1 H, HCº), 2.48 (td, ³
J = 7.6
Hz, 4
J = 2.7
Hz, 2 H, CH2CºC), 2.84 (t, ³
J = 7.6 Hz,
2 H, CH2Ph), 7.19-7.33 (m, 5 H, Ph). ¹³C
(67.9 MHz, CDCl3): δ = 20.5
(CH2CºC), 34.8 (CH2Ph), 68.9 (HCºC), 83.8 (CºCH),
126.3 (CH
p
), 128.4 (CH
o
and CH
m
),
140.4 (C
i
).
The high cost of the phosphazene bases
represents a drawback of our protocol. We thank the referees for
the respective comments. The manuscript describing a new straightforward
method for the synthesis of P1-bases is currently in
preparation.
