close

Вход

Забыли?

вход по аккаунту

?

Kinetic Acidity of Methine Protons and Carbonyl-Activated Methylene Protons.

код для вставкиСкачать
(t), 60.6 (t), 54.5 (d), 52.4 (s), 49.0 (s), 38.4 (s), 29.3 (t), 23.7 (t), 21.4 (q),
21.2 (4). 13.8 (9).
141 D. Spitzner, M. Bokel, A. Engler, Tetrahedron Lett., in press.
[Sl M. E. Jung, C. A. McCombs, J. Am. Chem. SOC.100 (1978) 5207; D.
Spitzner, Tetrahedron Lett. 1978, 3349.
Kinetic Acidity of Methine Protons
and Carbonyl-Activated Methylene Protons"*
By Okiko Miyata and Richard R . Schmidt*
We have introduced the substituted acrylic ester 1 as a
versatile synthon 3"l. Hence, the a,y,y-trisubstituted y-lactones (tetronates) 2 could be synthesized from 1 in two
by means of acetaldehyde and isobutyraldehyde
the y-substituted lactones 4a and 4b were synthesized in a
one-step reaction (Scheme 1).
2
aprotic media at the y-carbon atom or at the carbonyl oxygen atom. Surprisingly, the a-substituted products 8aA8aC and 8bA-8bC were obtained from 4a and 4b after
deprotonation with lithium diisopropylamide (LDA) in tetrahydrofuran (THF) and reaction with CH,OD, CH31, or
C2H5CH0.These products could also have arisen from the
y-deprotonated species 5a and 5b via 7aA-7aC and
7bA-7bC; to exclude this route 8bA was deprotonated
and treated with propionaldehyde; following work-up
with D20, however, no SbC-d, was formed.
In consequence, direct lithiation of 4a and 4b to afford
6a and 6b, respectively, must be assumed. Rapid H/D exchange in basic protic media was established through formation of 4b-d2 from 4b in NaOMe/MeOD.
These investigations show that in the LDA/THF system
the kinetic acidity of the a-vinyl protons of 4a and 4b is
greater than that of the carbonyl-activated y-methylene
protons, although abstraction of the latter would lead to
the resonance-stabilized oxapentadienyl anions 5a and 5b,
respectively. This result emphasizes the importance of the
direct deprotonation of inductively activated vinylic methine groups; of course, it is also important that the metalated species can be intramolecularly complexed['].
3
Received: March 30, 1982 [Z 172 IE]
German version: Angew. Chem. 94 (1982) 651
The complete manuscript of this communication appears in:
Angew. Chem. Suppl. 1982. 1398-1403
4 a , R = CH3 (47%)
"4; q
M e$
'0
0
L C s H ? (55%)
H R
Sa, b
6a, b
4b-dz
I
A 2,6-DiazasemibullvaleneX*
I
5.
4
Me0
Me0
R
7aA-C
7bA-C
[I] R. R. Schmidt, J. Talbiersky, P. Russegger, Tetrahedron Lett. 1979.
4273.
121 0. Miyata, R. R. Schmidt, Tetrahedron Lett. 23 (1982) 1793.
(31 N. G. Clerno, G. Pattenden, Tetrahedron Lett. 23 (1982) 585.
(41 a) A. Pelter, M. T. Ayoub, J. Schultz, R. Hansel, D. Reinhardt, Tetrahedron Lett. 1979, 1627; b) A. Pelter, R. Al-Bayati, W. Lewis, ibid. 23 (1982)
353.
Me0
H R
D
8a.4, 8aB, 8aC
8bA, 8bB. 8bC
8bC-dl
I
A , E = D; B, E = CH3; C , E = CH-CzH,
I
OH
Scheme I . a: LDA in THF, -9O"C, I h.-b: LDA in THF, -8O"C, 30
min.-c: 40 min at -8O"C, 30 min at -50°C: yield: quant. SaA, 61% SaB,
48% S a c , quant. SbA, 68% SbB, 56% 8bC.-d: 1 M NaOMe in MeOD, R. T.,
20 h; yield: quant. 4b-dz.
After deprotonation, the parent compound 4c - as
found by Pelter et aZ.[41-reacts with electrophiles in
By Christoph Schnieders, Hans-Josef AItenbach and
Klaus Miillen*
In the extreme case, lowering the energy barrier for the
degenerate Cope rearrangement in bullvalene, barbaralane, and semibullvalene systems leads to a "bishomoconjugated" ground state"]. According to theoretical considerations[", a ground state of this type occurs in semibullvalenes in which the CH groups in the 2- and 6-, or 3- and 7-,
positions have been replaced by N atoms[31.We have now
succeeded in synthesizing the first diazasemibullvalene
with which we have been able to test the predictions experimentally.
Our studies of the bisallyl system 3, which we obtained
by reductive cleavage of the ofrom the semibullvalene lLJ1
bond[51,indicated that the readily accessible diaza analogue 4 and the dihydro derivative 516]were suitable precursors for 2. 5 reacts with N-bromosuccinimide to afford a
mixture of the mono-, di-, and tribromides 6-8; according to the spectral data 7 is configurationally uniform.
[*] Prof. Dr. R. R. Schmidt, Dr. 0. Miyata
Fakultat fur Chemie der Universitat
Postfach 55 60, D-7750 Konstanz (Germany)
[**I Vinyl Carbanions, Part 15. This work was supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 0.
M . expresses thanks to the Alexander-von-Humboldt-Stiftung
for financial support-Part 14: 121.
Angew Chem Inf Ed Engl 21 (1982) No. 8
[*] Prof. Dr. K. Mullen, C. Schnieders, Dr. H.-J. Altenbach
Institut fur Organische Chemie der Universitat
Greinstrasse 4, D-SO00 Koln 41 (Germany)
[**I This work was supported by the Fonds der Chemischen Industrie. We
thank Priv.-Doz. Dr. J. J. Veith, TH Darmstadt, for the FD-MS measurements.
0 Verlag Chemie GmbH, 6940 Weznherm. 1982
0570-0833/82/0808-0637 $ 0 2 50/0
637
Документ
Категория
Без категории
Просмотров
0
Размер файла
114 Кб
Теги
acidity, protons, methylene, carbonyl, methine, kinetics, activated
1/--страниц
Пожаловаться на содержимое документа