Unexpected zirconium-mediated multicomponent reactions of conjugated 1,3-butadiynes and monoynes with acyl cyanide derivatives

Article abstract of DOI:10.1002/chem.201202607

Going ber(zirc): Zirconium-butadiyne complexes react with acyl cyanide derivatives through diverse reaction pathways. The complexes react with two molecules of carbamoyl cyanide to form 1,4-benzodiazepin-2-one-derivatives containing azazirconacycles. Reac

Full text of DOI:10.1002/chem.201202607

COMMUNICATION
DOI: 10.1002/chem.201202607
Unexpected Zirconium-Mediated Multicomponent Reactions of Conjugated
1,3-Butadiynes and Monoynes with Acyl Cyanide Derivatives
Shasha Yu, Xu You, and Yuanhong Liu*[a]
Five-membered group-4 metallacyclocumulenes, first re-
ported in 1994 by Rosenthal et al., have attracted much at-
tention owing to their fascinating structural features, their
uct derived from the addition of two molecules of aldehyde
to a metal-coordinated butadiyne complex.[6] In this commu-
nication, we report an unprecedented zirconium-mediated
multicomponent reaction of 1, 3-butadiynes with carbamoyl
cyanides to give azazirconacycles containing a 1,4-benzodia-
zepin-2-one skeleton; the cascade reaction involving an in-
À
unique M C bonding, and their unusual reaction proper-
ties.[1,2] These complexes can be synthesized through the
ligand-exchange reactions of 1,3-butadiynes with the alkyne
complexes [Cp2M(L)(h2-Me3SiCꢀCSiMe3)] (M=Ti, L =no
ligand; M=Zr, L=THF, pyridine),[1a] isomerization of bis-
À
teresting C H functionalization of N-aryl rings on carbamo-
yl cyanides. Herein, we also report the diverse reactivity of
these zirconacycles toward aroyl cyanides and alkyl cyano-
formates, the resulting reactions involving an insertion of a
cyanide group into the metal–butadiyne complexes as the in-
itial step (Scheme 1).[9] In addition, we show that this reac-
(C6F5)3,[2f,g] reduc-
ACHTUNGTRENNUNG(alkynyl)zirconocenes as catalyzed by BACHTUNGTRENNUGN
tion of dihalide metal complexes with magnesium in the
presence of diyne,[1a] and through light-induced rearrange-
ment of metallocene bisacetylides.[1a] X-ray crystal analysis
and theoretical calculations[3] of five-membered metallacy-
clocumulenes showed that a coordination between the cen-
tral double bond with the metal contributes to the remarka-
ble stability of these highly strained metallacycles. The
chemistry of metallacyclocumulenes developed by the re-
search groups of Rosenthal and Erker revealed that a varie-
ty of interesting reaction modes, such as complexations, re-
À
actions with Lewis acids, C C bond cleavage, and coupling
reactions are possible.[1a] Although much progress has been
achieved, the use of these metallacycles in organic synthesis
has far less been explored. For example, the reactivity of
five-membered metallacyclocumulenes toward carbon elec-
trophiles has rarely been studied; so far, only its reactions
[5]
with acetone[4] and CO2 have been reported, to the best of
our knowledge. Recently, we found a very convenient
method for the monozirconation of 1,3-butadiynes[6] contain-
ing bulky silyl- or tert-butyl substituents by direct reactions
of these butadiynes with the Negishi reagent without addi-
tion of any ligand or additives.[7,8] We suggested that five-
membered zirconacyclocumulenes were formed in these re-
actions, based on an NMR study of the zirconium intermedi-
ates and single-crystal X-ray analysis of [Cp2Zr(h4-1,2,3,4-
tBuC4tBu)]. These complexes undergo two sequential syn-
SE2’ reactions with various aldehydes to yield the cis-[3]cu-
mulenic diols, which represents the first example of a prod-
Scheme 1. Diverse types of reactivity of zirconocene–butadiyne com-
plexes.
tivity is also exhibited by zirconocene–monoyne complexes.
As demonstrated in our recent study,[6] treatment of 1,3-
butadiyne 1, which bears bulky silyl groups, with the Negishi
reagent resulted in the formation of zirconacyclocumulene 3
as a major product, which is possibly in equilibrium with the
three-membered alkynylzirconacyclopropene 2, although
the equilibrium lies predominantly on the side of 3. Interest-
ingly, 2/3 undergoes a novel reaction when treated with car-
bamoyl cyanides (Table 1). For example, addition of 3 equiv-
alents of Ph2NCOCN to the thus formed zirconacycle de-
rived from 1,4-bis(tert-butyldimethylsilyl)buta-1,3-diyne (1a)
followed by heating at 808C for 3 hours led to the formation
of five-membered a-alkynylazazirconacycle 4a incorporating
a 1,4-benzodiazepin-2-one skeleton in 48% yield (Table 1,
[a] S. Yu, X. You, Prof. Y. Liu
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Lu, Shanghai 200032 (P. R. China)
Fax : (+86)021-64166128
E-mail: yhliu@mail.sioc.ac.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202607.
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Table 1. Zr-mediated multicomponent reactions of 1,3-butadiynes with carbamoyl cyanides.
tries 1–10). The reactivity was
shown to be influenced by the
electronic effect of the arene
substituents. The use of sub-
strates containing either elec-
tron-neutral or electron-rich
substituents on the aryl ring
gave the corresponding prod-
ucts in yields ranging from 47–
60% yields (Table 1, entries 1–
5, 7–9). The use of electron-
Entry Diyne
R2(Ar)NCOCN
Ph2NCOCN
Product
Yield
[%][a]
1
4a 48[b]
poor
substrate
(p-
BrC6H4)MeNCOCN provided
4j in lower yield (37%; Table 1,
entry 10), presumably because
of the reduced nucleophilicity
of the aromatic ring. The struc-
ture of zirconium complex 4
was unambiguously confirmed
by X-ray crystallographic analy-
ses of 4d and 4j.[10] To under-
stand the possible side reac-
tions, the reaction of 1b with
Ph2NCOCN that was quenched
with aqueous 3N HCl was in-
vestigated. It was found that
enynyl amide 5 was formed in
27% yield, while the major
product 4b decomposed under
these quenching conditions
(Table 1, footnote of entry 2).
The results imply that a com-
petitive reaction pathway in-
2
3
4
Ph2NCOCN
Ph2NCOCN
Ph2NCOCN
R1 =TBDPS
R1 =TIPS
R1 =TPS
4b 60[c]
4c 53
4d 56
(p-
5
6
1b
1b
4e 55[d]
4 f 51
OMeC6H4)2NCOCN
(p-ClC6H4)2NCOCN
Ar=p-ClC6H4; X=Cl
7
1b
PhMeNCOCN
4g 50[e]
8
1b
1b
1b
(p-
Ar=p-MeC6H4; X=Me
Ar=p-OMeC6H4; X=OMe
Ar=p-BrC6H4; X=Br
4h 55
4i 47
4j 37
MeC6H4)MeNCOCN
(p-
OMeC6H4)MeNCOCN
9
10
ACHTUNGTRENNUNG
volving insertion of
a C=O
[a] Yields of isolated product. [b] R1 =TBS. [c] When the reaction was quenched by adding 3NHCl and the re-
sulting mixture was stirred overnight, amide 5 was isolated in 27% yield, whereas 4b had decomposed.
[d] Ar=p-OMeC6H4, X=OMe. [e] Ar=Ph, X=H. TBS=tert-butyldimethylsilyl, TBDPS=tert-butyldiphenyl-
silyl, TIPS=triisopropylsilyl, TPS=triphenylsilyl.
bond of carbamoyl cyanide also
occurs during the reaction. Ben-
zodiazepines are important het-
erocyclic compounds, which ex-
hibit a wide range of biological
activities and have emerged as
privileged scaffolds in drug dis-
covery.[11] 1,4-Benzodiazepin-2-
entry 1). Remarkably, in this transformation, two carbamoyl
cyanide units were incorporated into the products, and a
cascade sequence involving scission and recombination of
ones are well known for their anxiolytic, sedative, and anti-
convulsant activities (e.g. diazepam, bromazepam),[12] and
furthermore, they can also act as effective anticancer[13] and
protein-transferase inhibitors.[14] One of the most potent and
selective CCKB receptor antagonist is a 3,5-diamino-1,4-ben-
zodiazepines (Figure 1).[15] Our method provides a straight-
forward route to these heterocycles.
We also made an effort to employ aryl-substituted 1,3-bu-
tadiynes as substrates. However, without addition of any
ligand, the direct reaction of the Negishi reagent with 1,4-di-
phenyl-1,3-butadiyne in toluene resulted in the formation of
several products after quenching the mixture by 3N HCl and
allowing the mixture to stir overnight. To our delight, reac-
À
different chemical bonds and a C H bond functionalization
of one of the N-phenyl rings took place during the reaction
process. These metallacycles are quite stable towards air and
water, thus allowing facile separation using silica-gel column
chromatography. Representative results are shown in
Table 1. We first investigated the effect of silyl groups
(Table 1, entries 1–4), it was found that the best yield was
achieved using TBDPS-substituted butadiyne (1b, Table 1,
entry 2). A variety of carbamoyl cyanides including N,N-
diaryl, N-alkyl, and N-aryl substituted carbamoyl cyanides
underwent the reactions smoothly, furnishing the corre-
sponding products 4a–4j in 37–60% yields (Table 1, en-
tion of zirconocene–butene complex [Cp2Zr
ACHTUNGTRENUN(NG 1-butene)-
AHCTUNGTRENNUNG
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Zirconium-Mediated Multi-Component Reactions
COMMUNICATION
Figure 1. Biologically active 1,4-benzodiazepines.
with PMe3 at room temperature,[16] with diphenylbutadiyne
occurred efficiently to afford phosphine-stabilized zirconacy-
clopropene 6 in 82% yield, as determined using NMR spec-
troscopy; the compound can be isolated easily without
taking steps to avoid exposure to air and moisture. Interest-
ingly, only one regioisomer with respect to the orientation
of the PMe3 ligand was obtained; for this regioisomer, PMe3
is proximal to the alkynyl group.[10] Subsequent reaction of
6, which was generated in situ with Ph2NCOCN, delivered
Scheme 3. Possible reaction mechanism for the formation of complex 4.
À
leads to intermediate 14, C C bond fragmentation followed
by a 1,3-hydrogen shift furnishes the final product 4.
The above results inspired us to investigate the reactivity
of zirconacyclocumulenes 3 toward aroyl cyanides. The
proximity of the CO and CN groups in acyl cyanides enhan-
ces the electrophilicity of both functionalities. Although the
reactions usually occur at the carbonyl group,[19] attack at
the CN moiety by soft nucleophiles such as H2S[20] and
azides[21] are known. Here we found that the zirconium-
mediated reaction of TBS-substituted butadiyne 1a with
PhCOCN provided azazirconacyclopentene 16a in 29%
yield (Table 2, entry 1). The low yield in this case is due to
the partial elimination of the butadiyne ligand from the zir-
conium complex. Interestingly, employing either TBDPS or
TPS-substituted butadiynes afforded better yields (Table 2,
entries 2–13). The results indicated that a CN group reacts
preferentially with zirconacycle 2/3 at the initial step. The
reaction pattern is quite different compared with that of the
reactions of aroyl cyanides with seven-membered zirconacy-
clocumulenes, which were prepared by coupling of benzyne-
zirconocene with butadiynes.[7c] In those reactions, a carbon-
yl group reacted preferentially with a propargyl zirconium
moiety. The resulting azazirconacycle can be described by
the resonance structures of a Lewis formula (16) and a
seven-membered oxazirconacycle (16’; see scheme above
Scheme 2. Zr-mediated coupling reaction of 1,4-diphenyl-1,3-butadiyne
with Ph2NCOCN.
similar azazirconacycle 7[10] in 56% yield (Scheme 2).
For this novel transformation, we tentatively propose the
mechanism outlined in Scheme 3. First of all, an equilibrium
between zirconacyclopentatriene 3 and zirconacyclopropene
2 exists in the reaction mixture; 3 is likely to be the domi-
nant species, whereas 2 is more reactive.[6,7a] An SE2’-type
addition of the CN group of carbamoyl cyanides to the less
hindered propargyl zirconium moiety in complex 2 takes
place to deliver an azazirconacyclocumulene 8, which might
isomerize to azazirconacyclopentadiene 10; however, we
still cannot exclude the reaction pathway for 10 involving
À
Table 2) with an intramolecularly coordinated Zr N bond
according to X-ray crystal analysis of 16b.[10] We have re-
ported that azazirconacyclopentadienes produced through
coupling of alkynes with normal nitriles reacted with aroyl
cyanides to form 3-cyano-4,5-disubstituted-azazirconacyclo-
pentene.[22] The structure of 16 is similar to the one reported
for above-mentioned azazirconacyclopentenes. This reaction
was applicable to a large variety of aroyl cyanides. The elec-
tronic nature of the arene substituents have little effect on
this coupling reaction, and in all cases, moderate yields were
obtained. Substituents, such as OMe, Cl, Br, F, and CF3 on
the aromatic ring were well tolerated in the reaction, and
À
direct insertion of a cyano group into the Zr Csp2 bond close
to the R1 group of 2.[17] As a minor reaction pathway, addi-
tion of the C=O group of carbamoyl cyanides to zirconacy-
cle 2/3 affords either cyano-substituted oxazirconacycle 9 or
11; hydrolysis of 11 gives enynyl amide 5 through elimina-
tion of a cyano group.[7c] Attack of the nitrogen lone pair in
intermediate 10 to the CN moiety of a second molecule of
carbamoyl cyanide followed by intramolecular nucleophilic
addition provides fused oxirane intermediate 13;[18] ring
opening of the oxirane by the electron-rich N-phenyl ring
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Y. Liu et al.
Table 2. Zirconium-mediated multi-component reactions of 1,3-butadiynes with acyl cyanides.
CN group followed by isomeri-
zation gives five-membered
azazirconacyclopentadiene 19.
Attack of the nitrogen lone pair
of 19 to the carbonyl group of a
second molecule of acyl cyanide
leads to intermediate 20 and a
cyanide ion. The latter reacts
with iminium cation 20 to form
the observed product 16.
Entry
1
Diyne
R2
Ph
Product
Yield (%)[a]
29
16a
The above reactions have
been successfully extended to
monoynes. For example, reac-
tion of phosphine-stabilized zir-
conocene–alkyne complex 21
with Ph2NCOCN at 808C gen-
erated 22[10] in 83% yield. The
reaction of 21 with PhCOCN
afforded 23 in 44% yield
(Scheme 5). These results make
this chemistry very useful for
further applications.
16b
Ar=Ph
2
Ph
51
3
4
5
6
7
1b
1b
1b
1b
1b
p-MeC6H4
p-OMeC6H4
p-ClC6H4
p-BrC6H4
p-CF3C6H4
Ar=p-MeC6H4
Ar=p-OMeC6H4
Ar=p-ClC6H4
Ar=p-BrC6H4
Ar=p-CF3C6H4
16c
16d
16e
16 f
16g
42[b]
50
56
56
53
16h
Ar=Ph
8
Ph
52
To release the organic moiety
from the zirconium complexes,
we also carried out some deme-
talation reactions. Protonolysis
of the complex 4b with HCl/
Et2O solution gave heterocycle
24 in 97% yield. In the case of
zirconacycle 16b, gaseous hy-
drogen chloride was required
for demetalation. Surprisingly, a
9
1d
1d
1d
1d
p-MeC6H4
p-CF3C6H4
p-FC6H4
Ar=p-MeC6H4
Ar=p-CF3C6H4
Ar=p-FC6H4
Ar=2-furanyl
16i
16j
16k
16l
53
56
58
47
10
11
12
2-furanyl
13
1b
EtO
16m
69[b]
[a] Yield of isolated product. [b] Quenched with saturated aqueous NaHCO3.
thus products 16d–g and 16j and k were obtained in yields
ranging from 50–58% (Table 2, entries 4–7, 10, and 11). Het-
erocyclic acyl cyanides, for example, furan-2-carbonyl cya-
nide, reacted as well to give 16l in 47% yield (Table 2,
entry 12). Ethyl cyanoformate was also a good substrate and
the corresponding product, 16m, was obtained in a relative-
ly high yield (69%; Table 2, entry 13).
For the formation of 16, we propose the reaction mecha-
nism shown in Scheme 4. First, an SE2’-type addition of the
Scheme 5. The reactions of zirconocene–monoyne complexes.
novel cyclization/skeletal rearrangement reaction took place
to provide highly functionalized 2,5-diphenyloxazolo-
[5,4Àb]pyridine 25[10,23] in 69% yield, which is not easily
prepared using other methods (Scheme 6).
In summary, we have identified new reaction patterns for
both zirconocene–butadiyne and zirconocene–monoyne
complexes in the presence of acyl cyanide derivatives. These
transformations provide a series of functionalized heterozir-
conacycles through multicomponent reactions. Protonolysis
of the corresponding metallacycles allows for easy access to
diverse substituted 1,4-benzodiazepin-2-ones and novel
Scheme 4. Possible reaction mechanism for the formation of complex 16.
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Zirconium-Mediated Multi-Component Reactions
COMMUNICATION
c) X. Fu, J. Chen, G. Li, Y. Liu, Angew. Chem. 2009, 121, 5608;
Angew. Chem. Int. Ed. 2009, 48, 5500; d) J. Chen, Y. Liu, Tetrahe-
dron Lett. 2008, 49, 6655; e) Y. Liu, H. Gao, S. Zhou, Angew. Chem.
2006, 118, 4269; Angew. Chem. Int. Ed. 2006, 45, 4163.
[8] The reaction of the Negishi reagent with tBuCꢀC-CꢀCtBu has
also been reported. However, the desired zirconacyclopentatriene
could only be obtained in low yield; see: a) V. V. Burlakov, V. S.
Bogdanov, K. A. Lyssenko, L. I. Strunkina, M. Kh. Minacheva, B. N.
Strunin, U. Rosenthal, and V. B. Shur, Russ. Chem. Bull. 2010, 59,
668. For further studies, see: b) V. V. Burlakov, V. S. Bogdanov,
K. A. Lyssenko, A. Spannenberg, W. Baumann, P. Arndt, M. Kh.
Minacheva, L. I. Strunkina, U. Rosenthal, V. B. Shur, Izv. Akad.
Nauk SSSR, Ser. Khim. 2012, 163.
Scheme 6. Protonolysis experiments.
[9] For the reactions of zirconacyclocumulenes derived from coupling
reactions of benzynezirconocenes and 1,3-butadiynes together with
either carbamoyl cyanides, cyanoformates, or aroyl cyanides through
different reaction pathways, see Ref. [7c].
oxazolo
G
action mechanism and further application of this chemistry
are in progress.
[10] CCDC-871681 (4d, adduct containing one molecule of MeOH and
two molecules of CH2Cl2), 871684 (4j, MeOH adduct), 871685 (6,
C6D6 adduct), 871683 (7), 871682 (16b, CHCl3 adduct), 871680 (22),
and 871686 (25) contain the supplementary crystallographic data for
this paper. This data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax (+44) 1223–336–033; or deposit@ccdc.cam.ac.uk.
[11] D. A. Horton, G. T. Bourne, M. L. Smythe, Chem. Rev. 2003, 103,
893.
We thank the National Natural Science Foundation of China (Grant Nos.
21072208, 21125210, 21121062), Chinese Academy of Science, and the
Major State Basic Research Development Program (Grant No.
2011CB808700) for financial support.
[12] R. Mandrioli, L. Mercolini, M. A. Raggi, Curr. Drug Metab. 2008, 9,
827.
Keywords: alkynes
multicomponent reactions · zirconium
· cycloaddition · benzodiazepines ·
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Spannenberg, W. Baumann, U. Rosenthal, Organometallics 2002, 21,
1512.
[22] Y. Liu, B. Yan, Organometallics 2006, 25, 544.
[23] A possible reaction mechanism is given in the Supporting Informa-
tion.
[6] X. Fu, S. Yu, G. Fan, Y. Liu, Y. Li, Organometallics 2012, 31, 531.
[7] For related papers, see: a) X. Fu, Y. Liu, Y. Li, Organometallics
2010, 29, 3012; b) J. Chen, Y. Liu, Organometallics 2010, 29, 505;
Received: July 24, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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Y. Liu et al.
Multicomponent Reactions
S. Yu, X. You, Y. Liu* ....... &&&& — &&&&
Unexpected Zirconium-Mediated
Multicomponent Reactions of Conju-
gated 1,3-Butadiynes and Monoynes
with Acyl Cyanide Derivatives
Going ber
G
tives containing azazirconacycles.
complexes react with acyl cyanide
derivatives through diverse reaction
pathways. The complexes react with
two molecules of carbamoyl cyanide to
form 1,4-benzodiazepin-2-one-deriva-
Reactions with either aroyl cyanides or
alkyl cyanoformates lead to azazirco-
nacyclopentenes containing a quater-
nary carbon center.
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!