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1 1-Di- 1 2 3-Tri- and 1 1 4 4-Tetra-tert-butyl-1 3-butadiene.

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l,l-Di-, 1,2,3-Tri-, and 1,1,4,4-Tetra-tert-butyl1,3-butadiene**
H e n n i n g Hopf," Ralf H a n e l , Peter G. Jones: and
Peter Bubenitschek
Drdictrtrd to Profi.ssor Virgil Boekelheide
on rlie ocwsion of his 75th birrhdq
Highly substituted dienes exist predominantly in nonplanar,
and in the extreme case orthogonal, conformations, which in
turn result in chemical behavior distinctly different from that of
planar 1,3-dienes.['] Prerequisites for a systematic study of the
relationship between orthogonality and reactivity of di- and
polyenes are methods of synthesis that are not only efficient, but
also offer sufficient scope for application. Now. after we presented a procedure for the convenient preparation of highly alkylated 1.3-dienes that have trrr-butyl groups at C 2 and C 3 in 1991,
we describe new routes to terminal teri-butylated butadienes.
5,5-Dimethyl-4-tert-butyl-l.3-hexadiene
(3) is accessible by
the reaction of di-trrr-butylketone (1) with allylmagnesium bro-
Fig. I . The molecular structure O f 8 i n the
feliipproba-
El::)rspresent
advantageous (yield 63 Yo).3,6-Di-tert-butyl-2.2,7,7-tetramethyl3,S-octadiene (8) was finally obtained by reduction of the diol 7
with LiAIH,. All experiments afforded 8 as a mixture with the
[3]cumulene 9 and the ally1 alcohol 10 (typical composition of the
reaction mixture after a reduction period of 33
days: 3 % 7. 16% 10, 6 7 % 8 9. 13% unidentitied product; G C analysis).
Although the complete chromatographic separation/purification of these compounds has not
yet been successful, crystals that were suitable for
an X-ray crystal analysis[31could be picked out
manually. As Figure 1 shows, 8 has crystallographic inversion symmetry. The bond
lengths C I b C 2 (134.6(3) pm) and C2ZC2a
(135.3(4) pm) differ only marginally. The torsion
angle C3-C l-C2-C2a (- 179.3(4)':) and C 1-C2C 2 a - C l a (180") confirm the planarity of the
molecular
skeleton. The angle C 1-C 2-C 2a is
4
widened to 142.2(3)",[41which apparently in this
sterically strained system is easier to tolerate
than loss of planarity.
To gain a first impression of the reactivity of
the new dienes, whose structures can deduced
I
10
without ambiguity from the spectroscopic data
(Table l ) , we treated 6 with bromine in trichloro-
+
I
2
5
6
7
8
9
mide and dehydration of the resulting alcohol 2. Depending on
the reaction conditions. varying amounts of the Wagner-Meerwein product 4 are formed in this elimination: whereas this
1,5-hexadiene derivative arises exclusively with para-toluenesulfonic acid/benzene, the proportion when using thionyl chloride/
pyridine is only about 70 YO,and a virtual reversal of the product
ratio (89 % 3, 11 % 4, G C analysis) is achieved if 2 is initially
converted into its p-nitrobenzoate, and this ester is finally decomposed thermally ( 1 00 + 160 "C); 3 is obtainable in gram
quantities in this manner.
For the synthesis of (Z)-4-terr-butyl-2,2,6,6-tetramethyl-5methylene-3-heptene (6) the previously employed "terf-butylcuprate" method with diacetate 5 as starting material proved
[*] Prof DI H. Hopf. Dip].-Chem. R. Hlnel. Dipl.-Chem. P. Bubenitschek
Institut fiir Oi-ganische Chemie der Technischen Universitlt
Hagenring 30. D-38106 Braunschweig (FRG)
Telehx: Int. code + (531)-391-5388
Prot D I . P G. Jones
Instirut fiir Anorganische und Analytische Chemie
der Technischen Universitiit Braunschweig
[**I
Sterically Hindered Double-Bond Systems, Part 6. We thank the Deutsche
Forscliitngsgemeinschaft and the Fonds der Chemischen Industrie for the support of o u r research. Part 5 : H. Hopf. M. Traetteberg, R. Hlnel. Cliem. Brr..
in prey\.
Table 1. Spectroscopic data of 3. 6, and 8 [a]
3: ' H N M R (CDCI,): 6 =1.23. 1.36 (2 x s. each 9H. rBu), 5.03-5.09 (m. 2H. I - H ) .
6.02 ( d , J = 1 1 . 2 H z . 1H. 3-H). 6.93-7.03 (m, J = 11.2Hz. 1 H . 2-H); I 3 C N M R
(CDCI,):d=156.8(s.C-4),136.4.124.4(2xd.C-2.C-3).115.Y(t.C-l),38.7,37.7
(2 x s, C-5, C-7). 33.7. 31.8 (2 xq, CH,); UV (CH,CN): A,,,, (t) = 242 nm (8620):
IR (film): i. = 3087 cm-' (= CH,). 1620 (C = C). 901(> C = CHI): MS (70eV).
in/; ( Y o ) = I 6 6 (12, M ' ) . 109 (100). 57 (Y2);elementalanalysis forCILH2!(166.31):
calc. C86.67, H 13.33; found C86.58. H 13.31
6: ' H N M R (CDCI,): 6 = 1.04.1.08, 1.18 (3 x s, each 9 H . tBu). 4.76 (d. J = 1.8 HL
1 H . 8-H). 5.15 (d. J = l . Y Hz, 1 H. 8-H). 5.32 ( s . 1 H. 3-H): "CNMR (CDCI,):
6 =156.3. 146.2 ( 2 ~ sC-4,
.
C - 5 ) . 135.2 (d, C - 3 ) . 114.3 (t, C-8). 36.2. 35.0. 33 4
(3 xs. C-2. C -6. C-9). 32.5. 31.6 (9. CH,): UV (CH,CN)- /,,
(I:) = I 9 5 nm
(13600); IR (film): ? = 3078 cm-' (= CH,), 901 ( > C = CH,): elemental analysis
for C,,H,, (222.41): cdlc. C86.40. H13.60; found C 86.38, H13.66
8 : (mixture with 9): ' H N M R (CDCI,): 6 = 1.23, 1.33 (2x s. each 18 H, IBu), 6.42
( s . 2 H . 4 - H , 5-H): I3CNMR (CDCI,): 6 =151.2 (s. C 3. C-6). 123.0 (d. C - 4,
C - 5 ) . 39.1. 37.2 ( 2 x s . C-2, C-7. C 9. C - l l ) , 32.74. 32.0 (4. C H , ) ; GC:MS
(40eV). nz/z ( X ) = 278 (2, M + ) , 165 (34). 109 (24). 57 (100)
12:'HNMR(CDCI,):6=1.05.1.18,1.22(3xs.each9H.fBu).5.3Y(s.1H,4-H),
6.28 (s, 1 H . I - H): "CNMR (CDCI,): 6 =154 1 . 140.0 (s. C-4. C 5). 137,9 (d.
C-8), 106.8 (d, C-3), 37.5. 36.1. 33.9 ( 3 x s . C - 2 , C 6, C - 9 ) . 32.2. 31.2, 2Y.Y
(3 x q, CH,); UV (CH,CN): L,,, (6) = I 9 4 nm (14400): IR (Film): P = 307X cm-.'
( O h ) = 302,'300 (2. M '),
?46;244(2).
(= CH,). 647 (C-Br): GC,:MS (40eV):
165(7). lOY(7). 57(100): elemental analysis for C,,H,,Br (301.31): calc. C63.7H.
HY.70; found C63.69. H9.55.
[a] The NMR spectra were recorded a t 400 MHz('H) and 100.6 MHL ("C).
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methane at 0-5 “C. Instead of the expected 1,2- and/or 1,4-adducts, the monobromide 12 in which the butadiene part has been
wtuined was isolated exclusively (yield 60 YO).
Synthesis and Ligative Behavior
of a Gallacyclopentadiene**
Alan H. Cowley,” FranGois P. G a b b a i ,
and Andreas Decken
~
11
-H+
Boracyclopentadienes (boroles) have been known for several
years“] and continue to attract attention, for example, as ligands.[’] However, surprisingly little information is available regarding the heavier group 13 metallacyclopentadienes. In fact,
structurally authenticated examples of such compounds are
confined to one aluminacyclopentadiene, which was isolated as
an Et,O adduct and as a Ni(cod) complex (cod = 1,5-cyclopentadiene).I3] We report here the synthesis and X-ray crystal
structure of the first neutral gallacy~lopentadiene[~l
and the
corresponding (q-C,H,)Co complex.
Since l-phenyl-2.3.4,5-tetramethy~boracyclopen~adiene
dimeri ~ e s , [it~was
] clear that the isolation of the desired gallium analogue demanded the use of a bulkier aryl group. Accordingly,
the zirconacyclopentadiene 1 16] was treated with Ar’GaC1, (Ar’
= 2,4,6-tB~,C,H,)~” in C6H6 solution. The reaction, which
takes place over a 48 h period at 25 T, affords a 73 YOyield of
gallacyclopentadiene 2.
H
Br
t
12
13
- ICpJrC1,I
To explain this observation we postulate an initial Br attack
at the sterically less hindered side of the less substituted double
bond of 6. Whether this forms a bromonium ion (11) or an
“open carbenium ion” (13,orthogonal ally1 cation) is unknown.
At any rate this intermediate cannot be captured by the usual
back-side attack because of extreme steric shielding. It can,
however, be stabilized by deprotonation to form 12. The tvar7.s
arrangement of bromine and tevr-butyl substituents in 12 is concluded from NOE difference measurements (Table 1). Thus 6
favors substitution (by addition/elimination) over addition. and
thus behaves regmerutivelj, like u clussical uvme.
Received: Fehruarq 4. 1993 [Z6669IE]
German version: Aiigebi. Cli[wi.1994. 106. 1444
[1] H. Hopf. M. Traetteberg. H. Lipka. Aiigcw. Chrm. 1994. 106, 232-233: Angew
Cliem. I n t . Ed. Engl. 1994. 33. 204-205.
[ 2 ] H. Hopf. H . Lipka. CIZPI~Z.
Ber. 1991, 124. 2075-2084.
[3] Crystal data for 8 : C,,H,,. PT. u = 609.8(2). h = 820.3(3), c = 1028.0(3) A.
a =75.73(2). /r = 85.71(2). 7 =71.47(2).. V = 0.4725(3) A’, Z = l . T =
- 100 ’C. A colorless prism 0.7 x 0.45 x 0.12 mm was mounted in inert oil (type
RS3000. Fa. Riedel de Haen). On a Siemens R3 diffractometer. 2736 intensities
(Mo,, radiation. .; =71.073 pm. 2H,,, = 55 -) were measured, of which 2151
were independent (R,,, = 0.017). The structure M B S solved with direct methods
and refined anisotropically on F z (program SHELXL-93. G. M. Sheldrick.
University of Gottingen). The final n.R(F2)value was 0.186. with a conventional
R ( F ) of 0.061. for 97 parameters. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-76344 EggensteinLeopoldshafen (FRG) on quoting the depository number CSD-4006x6 and the
journal citation.
[4] A reviewer pointed out that the wide angle Cl-C2-C2a could he a result of
disorder in view of the “large displacement parameters” of the atom C2. Such
effects are always possible in principle and cannot be completely ruled out here.
With a Cieu value of only 0.046 A’ for C2, however. we see no reason to expect
a particularly large error and also no chance to resolve any disoi-der.
*
Ar’-M
I
I
2,M=Ga
3. M = In
I
Ar’ = 2,4.6-tBu3C,H2: X = CI, Br
The proposed formula for 2 is consistent with elemental analysis data and with the observations that a) the base peak in the
CI mass spectrum corresponds to M ’ , b) no peaks are detectable at higher m!z values (Table l ) , and c) ‘H and 13CNMR
spectra exhibit the anticipated resonances in the appropriate
intensity ratios (Table 1).
An X-ray structure analysis of 2[*lshowed that the asymmetric unit contained two independent molecules. However, the
metrical parameters for molecules 1 (Fig. 1) and I1 are very
similar and neither molecule exhibits unusually short intermolecular interactions. The five-membered gallacyclopentadiene ring
is planar. the maximum deviation from the least-squares plane
being 0.013 A for C(21). The Ar’Ga group is bonded to the
tetramethylbutadiene moiety in a symmetrical fashion such that
the endocyclic bond angle is about 45” smaller than the exocyclic
angles. The Ga-C(ary1) bond is slightly shorter than the other
two Ga-C bonds; however. all three distances fall in the range
for single bonds. The double bonds within the gallacyclopentadiene ring are localized as indicated by the fact that the C(20)C(21) distance is considerably larger than the other two C-C
distances. A further interesting feature of the structure of 2
relates to the near orthogonality of the Ar’ and gallacyclopentadiene rings (dihedral angles = 83.6 and 84.4‘ in molecules I and
[*] Prof. A. H. Cowley. F. P. Qahbai. Dr. A Decken
[**I
Department of Chemistry and Biochemistry
The University of Texas a t Austin
Austin. TX 78712 (USA)
Telefax: Int. code + (512)471-6822
This work was supported by the National Science Foundation aiid the Robert
A. Welch Foundation.
33;94:/313-/370 S 1 0 OO+.25:0
Angew. Chrm. b i t . Ed. Engl. 1YY4. 33. N o . 13
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