Job/Unit: O20278
/KAP1
Date: 19-04-12 15:04:35
Pages: 8
J. J. Eisch, K. Yu, A. L. Rheingold
FULL PAPER
95% ethanol yielded pure 8 (0.95 g, 95%), m.p. 200–201 °C. The
1H and 13C NMR spectra and the IR spectra in CHCl3 and in
Nujol mull have verified the identity of this solid with the pre-
tallization from absolute ethanol gave yellow crystals of 21, m.p.
209–211 °C. Whether the benzyl group has been added exo or endo
to the C6-position remains to be established by a future XRD
study. However, the 1H and 13C NMR and the IR spectra are in
complete accord with the structural connectivity of the structure
of 21. Finally, since compound 21 has not previously been reported,
the high-resolution mass spectrum of protonated 21 has been re-
corded and its mass of 451.2167 compares favorably with the theo-
retical mass for protonated 21 of 451.2169 with a delta of –0.4 ppm
and a composition of C33H27N2. Selected IR (CHCl3) absorptions:
3400 cm–1 (H–N) and 1635 cm–1 (C=N) (cf. Supporting Infor-
mation).
viously reported compound 8.[5] Moreover, the herein reported 13
C
NMR spectrum in CDCl3 and the XRD data on a pure, crys-
tallized sample of 8 lend strong corroboration for the 3D structure
of 8 both in the solid state and in solution. The solid-state structure
of 8, along with representative bond lengths and bond angles is
presented in Figure 1. In a reaction between 5 and lithium metal
pieces in THF, conducted in the same manner and on a similar
scale, the yield of 8 was likewise 95%. CCDC-868360 (for 8) con-
tains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. The
Supporting Information has reproductions of the 1H and 13C
NMR spectra, the IR spectrum, and the 3D structure of 8.
Reaction of 6,12-Diphenyldibenzo[b,f][1,5]diazocine (5) with the
Benzyllithium (15a)-TMEDA Complex in Toluene (Reaction Molar
Ratio of 5/15a = 1.0:2.2) The foregoing reaction was duplicated in
an identical manner and on the same scale, except that the reaction
molar ratio of 5/15a was 1.0:2.2. Although the purpose of this reac-
tion had been to achieve the bis-benzyllithiation of both C=N
bonds of 5, the surprising result was that the products now con-
sisted of a mixture of 55% (0.46 mmol) of monobenzyl adduct 21,
45% (0.040 mmol) of indolo[3,2-b]indole 8, and 0.40 mmol of bi-
benzyl (ratio of 8/bibenzyl = 1.0:1.0).
Reaction of 6,12-Diphenyldibenzo[b,f][1,5]diazocine (5) with Trityl-
lithium (15c): To
a deep-red solution of trityllithium (15c;
0.62 mmol, 2.2 equiv.) in THF (15 mL) was added a solution of 5
(100 mg, 0.28 mmol, 1.0 equiv.) in THF (5 mL). The resulting black
solution was stirred at reflux for 48 h. Thereupon addition of water
and usual workup gave a pale yellow product (550 mg). Analysis
by 1H NMR spectroscopy revealed the absence of any 5 and the
presence of indolo[3,2-b]indole (8; 100 mg, 0.28 mmol) and (4-
benzhydrylphenyl)triphenylmethane (20; 120 mg, 0.25 mmol) in a
1.0:0.90 molar ratio. In addition, only triphenylmethane was pres-
ent. The components of the reaction mixture were readily separated
by column chromatography on silica gel (hexane/ethyl acetate).
When the reaction run of such a reaction at a 1.0:2.2 ratio was
heated for 24 h at reflux and then worked up after hydrolysis, the
starting diazocine 5 was found to have been converted quantita-
tively into indolo[3,2-b]indole 8 quantitatively (0.86 mmol). In ad-
dition, bibenzyl (0.86 mmol) was found as the byproduct.
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Pure samples 8 and 20 were identified by comparing their H and
13C NMR spectra with those of authentic samples (cf. Supporting
Information).
When this reaction between 5 and 15a in a 1.0:2.2 molar ratio in
THF was repeated on the same scale and procedure at room tem-
perature but with benzyllithium made by the Gilman method, the
products were 36% of 8, 36% of bibenzyl, and 64% of 21. Heating
at reflux yielded an uninformative mixture of 8, 21, and 17, the last
resulting from the attack of 15a on THF.
Reaction of 6,12-Diphenyldibenzo[b,f][1,5]diazocine (5) with Benz-
hydryllithium (15b) at a Temperature of –78 °C to Room Tempera-
ture: To an orange-red suspension of benzhydryllithium (15b;
2.3 mmol, 2.0 equiv.) in THF (15 mL) stirred at –78 °C was added
a solution of 5 (378 mg, 1.06 mmol, 1.0 equiv.) in THF (5 mL).
After 2 h at –78 °C the reaction mixture was brought to room tem-
perature and allowed to stir for 16 h. Usual hydrolytic workup gave
the crude organic product (940 mg), whose 1H NMR spectroscopic
analysis showed the absence of 5 and the presence of indolo[3,2-b]
indole (8, 1.06 mmol) and 1,1,2,2-tetraphenylethane (14a) in a
1.0:0.92 ratio. Noteworthy also was the absence of 5,5-diphenyl-1-
pentanol (17), as indicated by TLC or by 1H and 13C NMR analy-
ses. Pure samples of products 8 and 14a were compared with au-
Reductions of 6,12-Diphenyldibenzo[b,f][1,5]diazocine (5) to 4b,9b-
Diphenyl-4b,5,9b,10-tetrahydroindolo[3,2-b]indole (8) by Grignard
Reagents in Refluxing Tetrahydrofuran – An Exploratory Survey:
The prototype for these reactions is the reaction of one equiv. of 5
with 2.2 equiv. of benzylmagnesium chloride in THF. Thus, a solu-
tion of 5 (358 mg, 1.0 mmol, 1.0 equiv.) in THF (20 mL) was
treated with benzylmagnesium chloride (2.0 m in THF, 1.15 mL,
2.23 mmol, 2.2 equiv.) at room temperature. The resulting bright
yellow solution was heated at reflux for 48 h and then hydrolytically
worked up and the organic products analyzed by 1H NMR spec-
troscopy. Starting 5 had been converted into 8 in 40% yield and
about 1% of 6-benzyl adduct 21 had been formed. Finally, bibenzyl
had also been generated, about in an equimolar amount,
0.40 mmol, to the 8 formed.
1
thentic samples by H and 13C NMR spectroscopy (cf. Supporting
Information).
When the foregoing reaction of 5 with 15b in THF was carried out
with the same ratio and concentration of reactants but at reflux for
48 h, 84% of the reactants were converted into 8 and 14a and about
30% of the THF was converted into the known 5,5-diphenyl-1-
pentanol (17) by the balance of reagent 15b.
Strictly in accord with the reaction of 5 with 2.2 equiv. of the benzyl
Grignard reagent, the following magnesium reagents gave the fol-
lowing conversions of 5 into 8 in THF: (1) Allylmagnesium chlor-
ide: 25% of 8 and 85% of 6-allyl-6,12-diphenyl-5,6-dihydrodi-
benzo[b,f][1,5]diazocine, having appropriate 1H and 13C NMR
spectra, whose XRD and 3D stereochemistry is currently under
investigation. (2) tert-Butylmagnesium chloride: 6% of 8 (lab light).
(3) tert-Butylmagnesium chloride: 15% of 8 (75 W unfrosted light,
external to the flask).
Reaction of 6,12-Diphenyldibenzo[b,f][1,5]diazocine (5) with the
Benzyllithium (15a)-TMEDA Complex in Toluene (Reaction Molar
Ratio of 5/15a = 1.0:1.1) To a yellow suspension of the benzyllith-
ium-TMEDA complex (1.90 mmol) in toluene/hexane (6.0 mL) at
–78 °C was added a solution of 5 (620 mg, 1.70 mmol) in THF
(5 mL), which generated a reddish black solution. After stirring
for 2 h at –78 °C, the mixture was then allowed to come to room
temperature over 12 h. Usual workup was carried out with the ethyl
ether and water. Based on the 1H NMR spectrum of the crude
product, 95% of diazocine 5 had been converted into 6-benzyl-
6,12-diphenyl-5,6-dihydrodibenzo[b,f][1,5]diazocine (21). Recrys-
Supporting Information (see footnote on the first page of this arti-
1
cle): Copies of the H and 13C NMR spectra, DEPT-NMR spec-
trum, IR spectra, high-resolution mass spectrum.
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