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Electrophilic Cyclodimerization of tert-Butylacetylene with Hydrogen Chloride.

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Electrophilic Cyclodimerization of
teut-Butylacetylene with Hydrogen Chloride111
7H3
IIC-C-C-CH,
I
I,+
By Kurl Griesbaum, Zillur Rehman, and
Uwe-Ingomar Zrihorszky 1*I
Reaction of tert-butylacetylene ( I ) with anhydrous hydrogen chloride a t room temperaturer21 leads to the normal
adducts (3) and (41,and to the adducts ( 6 ) and (71, which
are formed by a 1,2-methyl shift to the vinyl cation (2).
Besides these, the gas chromatogram of the crude adduct
mixture showed the presence of a few additional components, but only in the amount of or less than 1 % each.
(/)
CH3
1
Two of these unknown components, having higher retention times in the gas chromatogram than either of the
diadducts (41,(6),or (7), were of interest from the point
(5)
of view of a possible cyclocimerization. We have been able
H3C
CH3
to isolate both components as crystalline, colorless subHzE stances by a combination of fractional distillation and
preparative gas chromatography (3 m Carbowax-2OM
i
column).
The substance having the higher retention time (67 min)
has a m.p. 175-177 "C and its mass spectrum contains a
Cl
H,C CH,
molecular ion triplet typical of dichloro compounds a t
I
I
m/e = 236, 238, 240 corresponding to the empirical formula
C1 CH3
CIZH22C12, i.e. to a n adduct of two molecules of HCI and
I t
two molecules of tert-butylacetylene. An intense doublet at H, C - C -C - C H,
I I
m/e = 118, 120 (M/2) indicates ready splitting of the moleC1 CH3
CH, CH,
cule into two equal fragments and thus t o the presence of a
I
I
symmetrical cyclic structure. Further typical fragment ions
(4)
occur a t m/e = 200, 202 (M - HCI), m/e = 185, 187
(M - CH3 - HCI), m/e = 165 (M - HCl- CI), m/e = 103,
105 (M/2- CH3), m/e = 57 (tert-butyl), and m/e = 56
(isobutene).
To the best of our knowledge, the synthesis of ( 9 ) and (10)
The N M R spectrum (CC14) showed a singlet a t 6 = 1.02
represents the first case of a merely acid-catalyzed cyclodippm and a four-line pattern centered a t 2.79ppm i n the
merization via vinyl cations, in which n o isomerization of
intensity ratio 9 :2. The four-line pattern is obviously due
the acetylenic substrate t o allenic structures can occur.
t o a AA'BB' system (JAB = 13 Hz), whose individual
signals are further split by a small- presumably diagonalReceived: August 21, 1970
IZ 270 IEl
coupling of ca. 3 Hz.
Revised: September 14, 1970
I =tH31
6
This data is in accord with the structure of a cis-l,3-ditert-butyl-1,3-dichlorocyclobutane (9), which was supported by
of the N M R spectrum with that
of the corresponding cis-1,3-dichloro-1,3-dimethylcyclobutane 131.
The second component, i.e. the substance having the lower
retention time (48 min), has a m.p. 115-118"C and shows
the same signals in the mass spectrum as ( 9 ) although with
different relative intensities, The N M R spectrum showed
only two singlets a t 6 = 1.12 ppm and 6 = 3.01 ppm in the
intensity ratio 9 :2. This data is consistent with the strutture of the trans-compound (10) which is isomeric with ( 9 ) .
These investigations indicate that three reaction routes are
open to the vinyl cation (2): a) simple combination with C1ions Or with
and HCI to give the
(3)
and ( 4 ) ; b) rearrangement to the resonance-stabilized ally1
cation (5) r41; and c) cycloaddition to form the ally1 cation
(8) with subsequent formation of ( 9 ) and (10).
812
German version: Angew. Chem. 82, 841 (1970)
-~
[*I Priv.-Doz. K. Griesbaum and Dipl.-Chem.
Z. Rehman
Engler-Bunte-Institut fur Mineralol- und Kohleforschung
der Universitat
Dr. U. I. Zahorszkv
Institut fur Organische Chemie der Universitat
75 Karlsruhe 1 (Germany)
[11 This work was supported by the Deutsche Forschungsgemeinschaft and the Badische Anilin- und Soda-Fabrik, Ludwigshafen/Rh.
[21 K . Griesbaum and Z . Rehman, J. Amer. chem. SOC.92, 1416
[3] K . Griesbaum, W. Naegele, and G. G. Wanless, J. Amer.
them. sot. 87, 3151 (1965).
[4] In the meantime this rearrangement has also been observed
at a vinyl cation of structure (2) generated by solvolysis: H . G.
Martinez, M . Hanack, R. H , Summerville, P. Y. R.Schleyer, and
P.Slang, Angew. Chem. 82, 323 (1970); Angew. Chem. internat.
Edit. 9, 302 (1970).
Angew. Chem. internal. Edit.
/ Vol. 9 (1970) j' NO. I 0
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hydrogen, electrophilic, cyclodimerization, tert, chloride, butylacetylene
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