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Alkynylbenzocycloalkenes and trialkynylbenzenes by cyclodimerization and cyclotrimerization of α, ω-dialkynes using mesitylene-solvated cobalt atoms as catalytic precursor
155
A~y~yI~~~~~loalkenes and ~~lkynylbenze~es by Cyclod~~~atio~ and Gyclo~ime~i~ation of (x, o-dialkynes using ~esitylene-solvated Cobalt Atoms as Catalytic Precursor
There is current interest in robot-mediated formal [2+2+2] ~~~~o~~tions of unsaturated moieties as a powerful synthetic method [I]. We recently reported that arene-solvated cobatt atoms, obtained by reaction of Co vapour and arenes, are able to promote an unusual cocyclization of a, CJdialkynes and nitriles to alkynylMsubstituted pyridines [ 21. In our efforts to obtain additional data on the distinguishing features of such solvated Co atom-delved catalysts, we investigated their catalytic activity in the oligomerization of a, odialkynes. cfl,o-Dialkynes have been previously reported to give, in the presence of tr~sition metal catalysts, polymeric material andf or oligomers, with rather low selectivities [3 1. We found that, using as catafyk precursor mesityle~e-~lvated cobalt atoms obt~ed by ~o~onde~satio~ of Co vapour and mesitylene ]4], o, o-dialkynes arc selectively dimerized to I, and/or t~rne~~~ to ~kynylbe~~enes~ II ~ky~ylben~ocyclo~keues, ~~cheme 1). While the d~erizatio~ of cy, o-diynes to I has been often ob-
156
served before, their cyclotrimerization to trialkynylbenzenes, II, is very unusual [ 3 1. The results obtained in the oligomerization of 1,7-octadiyne and 1,8nonadiyne are reported in Table 1. The reaction takes place easily even at room temperature, and gives alkynylbenzocycloalkenes, I, and trialkynylbenzenes, II, in a ratio depending on the reaction temperature and on the nature of the diyne employed. Using 1,7-octadiyne, the annulated derivative is the main product in the range of temperature examined. 1,8-Nonadiyne gives at 25 “C almost only trialkynylbenzenes, II, while at higher temperature the annulated dimer I is also formed, to an extent lower than that observed using 1,7 -octadiyne. The trialkynyl benzenes are formed as 1,3,5- and 1,2,4- isomers with the asymmetrically-substituted species, IIb, as the major product. The regioselectivity of the reaction (IIb/IIa = ca. 2) is independent of the temperature. It is noteworthy that no significant amount of higher oligomers or polymers has been observed as reaction byproducts, contrary to reports using traditional catalytic precursors [ 31. The formation of I and II can be explained by assuming, according to the data reported in the literature [ 51, a reaction of the diyne with one or both the -yne functions to give the final products via the cobaltacyclopentadiene intermediates 1 and 2 (Scheme 2). The reasons why only one end of the cy,o-diyne molecule cannot usually react with such catalysts, affording II, are probably related to the nature of the catalytic precursor and are presently under investigation. The facile separation of I, IIa and IIb, and the absence of reaction byproducts make this catalytic process a very convenient route to prepare acetylene compounds which are of broad interest as useful intermediates and not otherwise easily accessible [ 61.
Experimental
Cobalt metal (0.05 g; 0.8 mg-atom) was evaporated during 40 min and cocondensed with mesitylene (30 ml) at liquid nitrogen temperature, using a glass metal atom reactor [ 71. The red-brown matrix obtained was warmed to ca. -40 “C and the resulting brown solution siphoned under nitrogen in a Schlenk tube and further handled at low temperature under inert atmosphere. Such a solution can be kept at low temperature (ca. -60 “C) for several days and used in catalytic runs in portions. In a typical run, 1,7octadiyne (4 ml, 30 mmol) was added, for instance, to half of this mixture and the thermally stable clear brown solution obtained was transferred into a 50 ml Pyrex Carius tube fitted with a Corning Rotaflo Teflon tap and warmed at 100 “C under stirring for 48 h. At the end of the reaction the unreacted dialkyne and the solvent were removed under vacuum, the crude product (2.74 g) was dissolved in n-pentane and chromatographed on alumina (activity II-III) to give hexynylbenzocyclohexene, I, by elution with n-pentane, (2.2 g; 10.4 mmol).
1
25 50 100
25 50 100
l,7-octadiyne
1,8-nonadiyne
Products ( %)b
60 82 86 traces 20 33
DiaIkyne conversion (%)
58 78 86
60 75 81
aDialkyne = 30 mmol; [Co] = 0.4 mg-atom; reaction time 48 h. bMolar composition determined on isolated products.
Temp. (“C)
of a, w-dialkynes catalyzed by mesityiene-solvated
Dialkyne
~ligomerization
TABLE Co atomsa
26 11 9 65 52 45
14 7 5 35 28 22
158
,I
159
pJ&+@d a
i
‘H NMR (300 MHZ, CDCls) 6 = 6.97 (d, Ji-i = 7.5 HZ, Hi); 6.89 (d, J&i = 7.5 HZ, Hi); 6.88 (s, Hh); 2.78 - 2.69 (m, H,); 2.55 (t, Jb_-f = 7.8 HZ, Hb); 2.21 (dt, J,, = 7.8 Hz, Jc--d = 2.7 Hz, H,); 1.93 (t, Jd- = 2.7 Hz, Hd); 1.83 - 1.65 (m, H, + Hf); 1.64 - 1.51 (m, Hg). MS: n/z, 212 (M+) By subsequent elution with pentane/ether 9/l, 1,3,5-trihexynylbenzene, IIa, (0.16 g; 0.5 mmol) and 1,2,4_trihexynylbenzene, IIb, (0.36 g; 1.14 mmol) were separated.
R
R = -CH,-CH,-CH,+2H,-C=CH
e
f
g
h
i
‘d R
‘H NMR (300 MHz, CDCl,) 6 = 6.82 (s, Hd); 2.58 (t, Je_f = 7.2 Hz, H,); 2.21 (dt, Jh3 = 6.6 HZ, Jh_i = 2.2 HZ, Hh); 1.95 (t, Jt_h = 2.2, Hi); 1.69 - 1.44 (m, Hf + Hg). MS: m/z, 318 (M+)
“a “b
R = -CH2-CH2-CH,-CH2--C-CH
e
f
g
h
i
‘H NMR (300 MHz, CDCl,) 6 = 7.06 (d, Ja+, = 7.8 Hz, H,); 6.95 (d, J,,_ = 7.8 Hz, Hb); 6.96 (s, H,); 2.68 (t, Je_f = 7.3 Hz, H,); 2.20 (dt, J,,* = 6.9 HZ, Jh+ = 2.2 HZ, Hh); 1.95 (t, Ji+ = 2.2 HZ, Hi); 1.59 - 1.37 (m, Hi + HA. MS: m/z, 318 (M+) The spectroscopic properties of the corresponding compounds obtained from 1,8-nonadiyne are quite similar.
160 References 1 See, for example, K. P. C. Vollhardt, Angew. Chem. bit. Ed. Engl., 23 (1984) 539 and references therein. 2 G. Vitulli, S. Bertozzi, M. Vignali, R. Lazzaroni and P. Salvadori, J. Organometall. Chem., 326 (198’7) C33. 3 E. S. Colthup and L. S. Meriwether, J. Org. Chem., 26 (1961) 5169; A. J. Hubert and J. Dale, J. Chem. Sot., (1965) 3160; K. P. C. Vollhardt, J. Am. Chem. Sot., 96 (1974) 4996. 4 J. R. Blackborrow and D. Young, in K. Hafner et al. (eds.), Metd Vapour Synthesis in Organometallic Chemistry, Springer Verlag, Berlin, 1979. 5 L. P. McDonnel Bushnell, E. R. Evitt and R. G. Bergmann, J. Organometall. Chem., 157 (1978) 445; J. P. Colman and L. S. Hegedus: Principles of Organotransition Metal Chemktry, University Science Books, Menlo Park, 1980; H. Bonnemann, Angew. Chem. Int. Ed. Engl., 17 (1978) 505. 6 A. J. Hubert, J. Chem. Sot. C, (1967) 6, 11,13; see also K. J. Vollhardt, Act. Chem. Res., 10 (1977) 1. 7 K. J. Kiabunde, P. Timms, P. S. Skeli and S. T. fttel, Inorg. Synth., 19 (1979) 59.
A~y~yI~~~~~loalkenes and ~~lkynylbenze~es by Cyclod~~~atio~ and Gyclo~ime~i~ation of (x, o-dialkynes using ~esitylene-solvated Cobalt Atoms as Catalytic Precursor
There is current interest in robot-mediated formal [2+2+2] ~~~~o~~tions of unsaturated moieties as a powerful synthetic method [I]. We recently reported that arene-solvated cobatt atoms, obtained by reaction of Co vapour and arenes, are able to promote an unusual cocyclization of a, CJdialkynes and nitriles to alkynylMsubstituted pyridines [ 21. In our efforts to obtain additional data on the distinguishing features of such solvated Co atom-delved catalysts, we investigated their catalytic activity in the oligomerization of a, odialkynes. cfl,o-Dialkynes have been previously reported to give, in the presence of tr~sition metal catalysts, polymeric material andf or oligomers, with rather low selectivities [3 1. We found that, using as catafyk precursor mesityle~e-~lvated cobalt atoms obt~ed by ~o~onde~satio~ of Co vapour and mesitylene ]4], o, o-dialkynes arc selectively dimerized to I, and/or t~rne~~~ to ~kynylbe~~enes~ II ~ky~ylben~ocyclo~keues, ~~cheme 1). While the d~erizatio~ of cy, o-diynes to I has been often ob-
156
served before, their cyclotrimerization to trialkynylbenzenes, II, is very unusual [ 3 1. The results obtained in the oligomerization of 1,7-octadiyne and 1,8nonadiyne are reported in Table 1. The reaction takes place easily even at room temperature, and gives alkynylbenzocycloalkenes, I, and trialkynylbenzenes, II, in a ratio depending on the reaction temperature and on the nature of the diyne employed. Using 1,7-octadiyne, the annulated derivative is the main product in the range of temperature examined. 1,8-Nonadiyne gives at 25 “C almost only trialkynylbenzenes, II, while at higher temperature the annulated dimer I is also formed, to an extent lower than that observed using 1,7 -octadiyne. The trialkynyl benzenes are formed as 1,3,5- and 1,2,4- isomers with the asymmetrically-substituted species, IIb, as the major product. The regioselectivity of the reaction (IIb/IIa = ca. 2) is independent of the temperature. It is noteworthy that no significant amount of higher oligomers or polymers has been observed as reaction byproducts, contrary to reports using traditional catalytic precursors [ 31. The formation of I and II can be explained by assuming, according to the data reported in the literature [ 51, a reaction of the diyne with one or both the -yne functions to give the final products via the cobaltacyclopentadiene intermediates 1 and 2 (Scheme 2). The reasons why only one end of the cy,o-diyne molecule cannot usually react with such catalysts, affording II, are probably related to the nature of the catalytic precursor and are presently under investigation. The facile separation of I, IIa and IIb, and the absence of reaction byproducts make this catalytic process a very convenient route to prepare acetylene compounds which are of broad interest as useful intermediates and not otherwise easily accessible [ 61.
Experimental
Cobalt metal (0.05 g; 0.8 mg-atom) was evaporated during 40 min and cocondensed with mesitylene (30 ml) at liquid nitrogen temperature, using a glass metal atom reactor [ 71. The red-brown matrix obtained was warmed to ca. -40 “C and the resulting brown solution siphoned under nitrogen in a Schlenk tube and further handled at low temperature under inert atmosphere. Such a solution can be kept at low temperature (ca. -60 “C) for several days and used in catalytic runs in portions. In a typical run, 1,7octadiyne (4 ml, 30 mmol) was added, for instance, to half of this mixture and the thermally stable clear brown solution obtained was transferred into a 50 ml Pyrex Carius tube fitted with a Corning Rotaflo Teflon tap and warmed at 100 “C under stirring for 48 h. At the end of the reaction the unreacted dialkyne and the solvent were removed under vacuum, the crude product (2.74 g) was dissolved in n-pentane and chromatographed on alumina (activity II-III) to give hexynylbenzocyclohexene, I, by elution with n-pentane, (2.2 g; 10.4 mmol).
1
25 50 100
25 50 100
l,7-octadiyne
1,8-nonadiyne
Products ( %)b
60 82 86 traces 20 33
DiaIkyne conversion (%)
58 78 86
60 75 81
aDialkyne = 30 mmol; [Co] = 0.4 mg-atom; reaction time 48 h. bMolar composition determined on isolated products.
Temp. (“C)
of a, w-dialkynes catalyzed by mesityiene-solvated
Dialkyne
~ligomerization
TABLE Co atomsa
26 11 9 65 52 45
14 7 5 35 28 22
158
,I
159
pJ&+@d a
i
‘H NMR (300 MHZ, CDCls) 6 = 6.97 (d, Ji-i = 7.5 HZ, Hi); 6.89 (d, J&i = 7.5 HZ, Hi); 6.88 (s, Hh); 2.78 - 2.69 (m, H,); 2.55 (t, Jb_-f = 7.8 HZ, Hb); 2.21 (dt, J,, = 7.8 Hz, Jc--d = 2.7 Hz, H,); 1.93 (t, Jd- = 2.7 Hz, Hd); 1.83 - 1.65 (m, H, + Hf); 1.64 - 1.51 (m, Hg). MS: n/z, 212 (M+) By subsequent elution with pentane/ether 9/l, 1,3,5-trihexynylbenzene, IIa, (0.16 g; 0.5 mmol) and 1,2,4_trihexynylbenzene, IIb, (0.36 g; 1.14 mmol) were separated.
R
R = -CH,-CH,-CH,+2H,-C=CH
e
f
g
h
i
‘d R
‘H NMR (300 MHz, CDCl,) 6 = 6.82 (s, Hd); 2.58 (t, Je_f = 7.2 Hz, H,); 2.21 (dt, Jh3 = 6.6 HZ, Jh_i = 2.2 HZ, Hh); 1.95 (t, Jt_h = 2.2, Hi); 1.69 - 1.44 (m, Hf + Hg). MS: m/z, 318 (M+)
“a “b
R = -CH2-CH2-CH,-CH2--C-CH
e
f
g
h
i
‘H NMR (300 MHz, CDCl,) 6 = 7.06 (d, Ja+, = 7.8 Hz, H,); 6.95 (d, J,,_ = 7.8 Hz, Hb); 6.96 (s, H,); 2.68 (t, Je_f = 7.3 Hz, H,); 2.20 (dt, J,,* = 6.9 HZ, Jh+ = 2.2 HZ, Hh); 1.95 (t, Ji+ = 2.2 HZ, Hi); 1.59 - 1.37 (m, Hi + HA. MS: m/z, 318 (M+) The spectroscopic properties of the corresponding compounds obtained from 1,8-nonadiyne are quite similar.
160 References 1 See, for example, K. P. C. Vollhardt, Angew. Chem. bit. Ed. Engl., 23 (1984) 539 and references therein. 2 G. Vitulli, S. Bertozzi, M. Vignali, R. Lazzaroni and P. Salvadori, J. Organometall. Chem., 326 (198’7) C33. 3 E. S. Colthup and L. S. Meriwether, J. Org. Chem., 26 (1961) 5169; A. J. Hubert and J. Dale, J. Chem. Sot., (1965) 3160; K. P. C. Vollhardt, J. Am. Chem. Sot., 96 (1974) 4996. 4 J. R. Blackborrow and D. Young, in K. Hafner et al. (eds.), Metd Vapour Synthesis in Organometallic Chemistry, Springer Verlag, Berlin, 1979. 5 L. P. McDonnel Bushnell, E. R. Evitt and R. G. Bergmann, J. Organometall. Chem., 157 (1978) 445; J. P. Colman and L. S. Hegedus: Principles of Organotransition Metal Chemktry, University Science Books, Menlo Park, 1980; H. Bonnemann, Angew. Chem. Int. Ed. Engl., 17 (1978) 505. 6 A. J. Hubert, J. Chem. Sot. C, (1967) 6, 11,13; see also K. J. Vollhardt, Act. Chem. Res., 10 (1977) 1. 7 K. J. Kiabunde, P. Timms, P. S. Skeli and S. T. fttel, Inorg. Synth., 19 (1979) 59.