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The synthesis of mixed geminal organometallic compounds
1966, PergsmonPressLtd. Tetrahedron LettersNo.25,PP. 2535-2538, Printedin GreatBritain,
THESYNTHESLSOFWIXEDG~OROANOMBTALL
IGGOMmmTS
GeorgeZweifelcud HenriArzoumuian Departmentof Uhemistry, Universityof GaJifornia Davis,cal.ifornia (Received17 March 1966)
Until
recently,the chemistryof geminaldimetallic canpoundshas re-
ceivedlittleattention.'The use of the hydroalmiuatichs and hydroboratl& reactions, however,has provideda new methodfox the preparation of difuuctional. orgauometallic coxpotmds.We have shomthatl-alkynes are readily convestedto l,l-diboroalhanes when treatedwith diborane. Thus hydroboration of l-pen-e or 1-hexynewith diboranein a 3 to 1 ratio gives804 of the correspondingl,l-diboroalhane. Use of dicyclohexylboraue or 2,3-dimethyl-2-butylboreneas hydroboratiug agentsresultsin essentially quantitative yieldsof the geminaldiboroucompounds. 4 The structures of the dihydroboration productswere established by their oxidationto E-peutauoic or n_husncic acid, respectively, when treatedwith ~-chloroperbenzoic a~id.~ In contrastto trialhylboraues, the geminaldiboroderivatives (1) react rapidlywith sodiumhydroxideto give cleavageof one carbon-boron bond. The enhancedreactivity may be attributed to stabilization of the incipientcarbanion(2) by interaction with the vacantp-orbitalof boron.4 Oxidationof the resultiugintermediate oxgauoboranes (1) with hydrogenperoxidegave 8~$ of primaryalcohols.
2535
2536
No.23
We have now found that l,l-diboropentane, derived from dihydroboration of l-pentyue with diborane, undergoes a similar, facile cleavage with sodium methoxide, lithium methoxide, butyllithium and methyllithium to give the l-boro-lsodio and the l-boro-1-lithio derivatives, respectively. The structures of these intermediates (4) were shown by their conversion to j-heptylborane (1) when treated with ethyl bromide. This organoboraue was not isolated but was oxidized directly to 3-heptanol (6).
Na,Li C&& \BJ \
/C2H5
C2HS~ -
C&&H 'B;
1. NeCH 2. w2
wkya5
OH
The experimental results are summarized in Table I. The possibility that a l,l-diboroalkane (1) was the precursor for the j-heptenol is ruled out since heating :.,l-diboropentanewith excess ethyl brcmide for 4 hours at 60" followed by hydrolysis and oxidation gave only l-pentenol. Moreover, evidence that l,l.-dilithiopentanewas not formede was shorn by the following experiment:
Treatment of 1,1-diboropentane in tetrehydrof'uranat 0' with a lCC$
excess of methyllithium followed by hydrolysis with 3N sedim hydroxide and oxidation with hydrogen peroxide gave 80% 1-pentanol. I&drolysis of a l,ldilithio derivative should have given only n-pentane. The fact that higher
yields of 3-heptanol are obtained with increasing amounts of methyllithium (Table I) suggests that part of the reagent must react with the alkylborane to form lithium tetraallqylboron.
TABLE1 fields of 3-Heptanol from 1-Sodio-l-boro- and 1-Lithio-1-boropentae
Reagent
Ratio Organoborane/ Reagent
Reaction 3-Heptanol,a,b Temp.,OC. %
NaOCH3
1:l
65
36
LiOCHs
1:l
o5
21
LiC&
1:l
25
55
LiCG
1:l
25
75
LiCHs
l:l.5
25
83
LiCHs
1:2
25
90
a Based on l,l-diboropentane. internal standard.
b
Determined by v.p.c. using an
To the best of our knowledge these results provide the first evidence of
the synthesis of a mixed geminal organometallic compound. Such derivatives, in which the two ligands exhibit large differences in reactivity, should be exceedingly useful in synthetic work.
Experiments designed to establish the
scope of this novel reaction and related transformations are currently underway.7
REFERENCES 1. 2.
I. T. Millar and H. Heaney, &art.
Rev. (London), l.l,I.09(1957). K. Ziegler, "Oraanometallic Chemistry," H. Zeiss, Ed., Reinhold Publishing Co., New York, N. Y., 1960.
3.
H. C. Brown, "Hydroboration," W. A. Benjamin, Inc., New York, N. Y., 1962.
4.
H. C. Brown and G. Zweifel, J. Am. Chem. Sot., 8&
3634 (1961).
No.23
5. G. Zweifrl and H. Arzoumanian, to be published. 6. It has been reported that l,l-diboron compounds, derived via hydroboration of l-alkynes with dicyclohexylborane, after treatment with excess butylllthium and followed by carbonation, yield malonic acid derivatives. G. Cainelli, C. da1 Ballo, and G. Zublani, Tetrahedron Letters, 3429 (1965). 7.
Research performed under a grant by the National Science Foundation.
THESYNTHESLSOFWIXEDG~OROANOMBTALL
IGGOMmmTS
GeorgeZweifelcud HenriArzoumuian Departmentof Uhemistry, Universityof GaJifornia Davis,cal.ifornia (Received17 March 1966)
Until
recently,the chemistryof geminaldimetallic canpoundshas re-
ceivedlittleattention.'The use of the hydroalmiuatichs and hydroboratl& reactions, however,has provideda new methodfox the preparation of difuuctional. orgauometallic coxpotmds.We have shomthatl-alkynes are readily convestedto l,l-diboroalhanes when treatedwith diborane. Thus hydroboration of l-pen-e or 1-hexynewith diboranein a 3 to 1 ratio gives804 of the correspondingl,l-diboroalhane. Use of dicyclohexylboraue or 2,3-dimethyl-2-butylboreneas hydroboratiug agentsresultsin essentially quantitative yieldsof the geminaldiboroucompounds. 4 The structures of the dihydroboration productswere established by their oxidationto E-peutauoic or n_husncic acid, respectively, when treatedwith ~-chloroperbenzoic a~id.~ In contrastto trialhylboraues, the geminaldiboroderivatives (1) react rapidlywith sodiumhydroxideto give cleavageof one carbon-boron bond. The enhancedreactivity may be attributed to stabilization of the incipientcarbanion(2) by interaction with the vacantp-orbitalof boron.4 Oxidationof the resultiugintermediate oxgauoboranes (1) with hydrogenperoxidegave 8~$ of primaryalcohols.
2535
2536
No.23
We have now found that l,l-diboropentane, derived from dihydroboration of l-pentyue with diborane, undergoes a similar, facile cleavage with sodium methoxide, lithium methoxide, butyllithium and methyllithium to give the l-boro-lsodio and the l-boro-1-lithio derivatives, respectively. The structures of these intermediates (4) were shown by their conversion to j-heptylborane (1) when treated with ethyl bromide. This organoboraue was not isolated but was oxidized directly to 3-heptanol (6).
Na,Li C&& \BJ \
/C2H5
C2HS~ -
C&&H 'B;
1. NeCH 2. w2
wkya5
OH
The experimental results are summarized in Table I. The possibility that a l,l-diboroalkane (1) was the precursor for the j-heptenol is ruled out since heating :.,l-diboropentanewith excess ethyl brcmide for 4 hours at 60" followed by hydrolysis and oxidation gave only l-pentenol. Moreover, evidence that l,l.-dilithiopentanewas not formede was shorn by the following experiment:
Treatment of 1,1-diboropentane in tetrehydrof'uranat 0' with a lCC$
excess of methyllithium followed by hydrolysis with 3N sedim hydroxide and oxidation with hydrogen peroxide gave 80% 1-pentanol. I&drolysis of a l,ldilithio derivative should have given only n-pentane. The fact that higher
yields of 3-heptanol are obtained with increasing amounts of methyllithium (Table I) suggests that part of the reagent must react with the alkylborane to form lithium tetraallqylboron.
TABLE1 fields of 3-Heptanol from 1-Sodio-l-boro- and 1-Lithio-1-boropentae
Reagent
Ratio Organoborane/ Reagent
Reaction 3-Heptanol,a,b Temp.,OC. %
NaOCH3
1:l
65
36
LiOCHs
1:l
o5
21
LiC&
1:l
25
55
LiCG
1:l
25
75
LiCHs
l:l.5
25
83
LiCHs
1:2
25
90
a Based on l,l-diboropentane. internal standard.
b
Determined by v.p.c. using an
To the best of our knowledge these results provide the first evidence of
the synthesis of a mixed geminal organometallic compound. Such derivatives, in which the two ligands exhibit large differences in reactivity, should be exceedingly useful in synthetic work.
Experiments designed to establish the
scope of this novel reaction and related transformations are currently underway.7
REFERENCES 1. 2.
I. T. Millar and H. Heaney, &art.
Rev. (London), l.l,I.09(1957). K. Ziegler, "Oraanometallic Chemistry," H. Zeiss, Ed., Reinhold Publishing Co., New York, N. Y., 1960.
3.
H. C. Brown, "Hydroboration," W. A. Benjamin, Inc., New York, N. Y., 1962.
4.
H. C. Brown and G. Zweifel, J. Am. Chem. Sot., 8&
3634 (1961).
No.23
5. G. Zweifrl and H. Arzoumanian, to be published. 6. It has been reported that l,l-diboron compounds, derived via hydroboration of l-alkynes with dicyclohexylborane, after treatment with excess butylllthium and followed by carbonation, yield malonic acid derivatives. G. Cainelli, C. da1 Ballo, and G. Zublani, Tetrahedron Letters, 3429 (1965). 7.
Research performed under a grant by the National Science Foundation.