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Carrol rearrangement on the surface of chromatographic grade alumina
Tetrahedron Letters,Vol.28,No.41,pp Printed in Great Britain
4893-4896,1987
0040-4039/87 $3.00 + .OO Pergamon Journals Ltd.
CARROL REARRANGEMENT ON THE SURFACE OF CHROMATOGRAPHIC GRADE ALUMINA S.I.Pogrebnoi, Y.B.Kalyan, M.Z.Krimer Institute of Chemistry, Grosul street, 3, Kishinev, USSR W.A.Smit*, Zelinsky Institute of Organic Chemistry, Leninsky pr. 47, Moscow, USSR
Abstract. Thermolysis on the surface of A1203 is proposed as a mild and con-
venient preparative method for /3,3/-sigmatropic Carrol rearrangement of acetoacetic esters of tertiary ally1 alcohols into respective )3&unsaturated ketones. As was reported earlier', the rate of intramolecular cyclization of dicobalthexacarbonyl complexes of allylpropargyl ethers into the derivatives of 3-oxabicyclo p,3,0]
octane (/2+2+1/ - cycloaddition, Khand-Pauson reac-
tion) is greatly enhanced provided the reaction is carried out in the absence of any solvents with the substrates applied to the surface of SiO2 or A120. This effect has been ascribed to the preferential stabilization of the coiled conformation of the adsorbed acyclic substrate due to the restrictions of its conformational mobility imposed by the interaction with the surface adsorption centers. It has been also suggested' that quite similar effects of the adsorption promotion should be operative in case of other antropy controlled intramolecular reactions. The present study has been undertaken to check the validity of this suggestion for the model example of Carrol reaction2a*b, a variant of /3,3/sigmatropic Claisen rearrangement2csd (Scheme I). Scheme 1
h I According to the conventional procedure Carrol reaction is carried
by a prolonged heating of the acetoacetic ester of ally1 alcohols (as a 4893
4894
neat liquid or in high boiling solvent) at 166-220=~~~~~. Recently the useful alternative to this thermal process has been developped3' involving the transformation of the starting J_under the action of 2 equiv. of LDA in THF3 into bis-enolate, The rearrangement of the latter was found to proceed in refluxing THF giving the respective y,a-unsaturated ketones 2
in good yields.
Our first attempts to carry out transformation 1 -2
on the surface
of the adsorbent met with little success. Thus when acetoacetate of dimewas adsorbed on Si02 (Woelm, 5/4OH
thylvinyl carbinol 3
or florisil (Ser-
va, 40/1OOp) and heated at 600~ for 2-5h, tic data indicated the complete disappearance of 2,
but the analysis of the resulting mixture (after elu-
tion with ether) revealed the presence of only trace amounts of the desired 6-methylhepten-5-on-2 2 cohol 2
the main product being acetoacetate of prenyl al-
isolated in 70% yield'. Thus under these conditions acylotropic
migration took place instead of /3,3/-rearrangement. Scheme 2
Me
Me
‘j”2 l
60’
Me rd0
Me-470de Me
0 la
0 3a
Rather unexpexedly but very rewarding it ha‘sl3eenfound that the use of AI 0 23
instead of Si02 caused a dramatic change in the course of the re-
action and under essentially the same conditions of the thermolysis (60oC, 3h) -la is converted completely into &4
(isolated yield 84%)5,6. Scheme 3
Me
-.
Me
Me0 rP 0
0 la
*$*3 *MeeoMe Me 2a
Acetoacetates of various tertiary ally1 alcohols -lb-e when applied to the surface of A1203 underwent similarly effective Carrol rearrangement leading to the formation of the expected ketones -_ 2b-e in good yields.415 Typical experimental procedure: _'& (l.Og, 4.2 mmol) in hexane (30 ml) was mixed with Al 0 (Woelm, basic, 5/40/J,log), the solvent was removed 23 on a rotovap at 20°C (30 mm Hg) and the resulting powder was heated at 600~ for 5 h (tic control indicated the complete absence of the starting mate-
4895
rial). Elution with hexene, followed by the removal of the solvent and distillation of the residue gave geranylacetone, 3
(0,62g, yield 75%) as a
mixture of E/Z isomers (E:Z=3:2, glc, pmr), b.p. 130-132O (20 mm Hg), I$
b
74-78%
(b) RI= Me, (c) R1 = Me, (d) RI= Me, I c\ Trial(%&%%e~~
lb-e 2b-e R2= Et R2= Me2C=CHCH2 R2= Me2CzCHCH2C(Me)=CHCH2(E) \
fevd$l.%2&t
chromatographic grade Al 0 from va23 riOUS sources (WOelm, FRG; Reanal, Hungary; Chemapol, CSSR; neutral, basic or acidic) differs very little (if any) in transformation 1 _3
its
ability to promote the
2. However the changes in ratio (r) A1203: J_produce
a profound effect on the rate of this conversion. Thus the thermolysis of 2
under standard conditions (600~, 2h) lea to the formation of
(isolated): 75% (;=30), 50%(~=10) and 14% (~=5), the rest being the starting material. It is known that acetoacetic esters of the secondary and especially of the primary ally1 alcohols are less prone to undergo Carrol rearrangement2b and in these cases
the target ketones are formed in modest yields. The at-
tempts to carry out these reactions on Al203 have shown
that: (i) the es-
ters of primary alcohols are not converted into respective ketones after heating at 600~ for 3-6h, while at the elevated temperature (90-IOOO) they are decomposed into the mixture of low boiling hydrocarbons; (II) esters of the secondary alcohols underwent Carrel rearrangement upon the heating in the adsorbed state (on A1203), but the yields of the products me low (e.g. If __L
2f, scheme 5).
Ph
A1203 r@
HO
0
O!f
6a”
rather
Scheme 5
* Phe
Me H
0
45%
2f (E)
Albeit the limitations mentioned the main result of the presented stu-
4896
dy seems to be indisputable: the use of A1203 as a dry media for /3,3/ sigmatropic Carrol rearrangement allows to carry out this reaction at much lower temperatures than those used in classical liquid phase procedure (60-70° instead of 160-220~). This effect seems to be very similar to that observed for the I-
1
rearrangement via bis-enolate induced by the action of the strong base' (vide supra). Hence it was tempting to speculate about a somewhat similar activation of 1 on A1203 due to the presence of Lewis acid and base sites on its surface. However at present we were unable to find any experimental evidence supporting this view'. Hence we prefer the explanation of the phenomena of the rate enhancement of /3,3/ sigmatropic rearrangement on A1203 to be given in the same terms of the adsorption promoted conformational changes of the substrate as had been advanced earlier'. Data presented in this paper taken together with the previous result provide a convincing evidence to the importance of the adsorption as an 8 emerging effective tool for the promotion of the organic reactions and attest to the tremendous potential of the further studies in this field. References 1. S.O.Simonian, W.A.Smit, A.S.Gybin, A.S.Shashkov, G.S.Mikaelian, V.A.Tarasov, I.I.Ibragimov, R.Caple, D.E.Froen, Tetrahedron Lett., 3, 1245 (1986). 2.(a) M.F.Carrol, JOChem.Soc,, 1940, 704; for a review see, (b) L.A.Yanovskaya t'Carro1Reaction", in "Reakzii i methodi issledovaniya organicheskih soedinenii", ~01.12, p.259, Izdatelstvo chimicheskoi literatury, Moscow) 1963; (c) G.B.Bennett, Synthesis 1971, 589; (d) Organic Reactions, vo1.22, p*l. 3. S.R.Wilson, M.F.Price, J.Org.Chem. 49, 722 (1987). 4. All products2rre identified by the comparison with the authentical samples (b.p., nD, glc, PMR); 2b,d,& are formed as E:Z mixtures (3:2). 5. Yields referred to the distilled product. 6. Under classical conditions of Carrol rearrangement could be prepared with the same yield but after heating at 140-160~ for 5h (see for example, W.Kimel, N.N.Sax, S.Kaizer et al., J.Org.Chem., 23, 153 (1958). 7. In this respect it is to be noted, that A1203 pretreated with base (tert.-BuOK or CH30Ha) did not reveal any enhanced activity in the promotion of & 3 conversion. 8. An interesting review covering some aspects of the problem has recently been published by P.Laszlo in Acc.chem.Res. 2, 121 (1986). (Received in UK 29 July 1987)
4893-4896,1987
0040-4039/87 $3.00 + .OO Pergamon Journals Ltd.
CARROL REARRANGEMENT ON THE SURFACE OF CHROMATOGRAPHIC GRADE ALUMINA S.I.Pogrebnoi, Y.B.Kalyan, M.Z.Krimer Institute of Chemistry, Grosul street, 3, Kishinev, USSR W.A.Smit*, Zelinsky Institute of Organic Chemistry, Leninsky pr. 47, Moscow, USSR
Abstract. Thermolysis on the surface of A1203 is proposed as a mild and con-
venient preparative method for /3,3/-sigmatropic Carrol rearrangement of acetoacetic esters of tertiary ally1 alcohols into respective )3&unsaturated ketones. As was reported earlier', the rate of intramolecular cyclization of dicobalthexacarbonyl complexes of allylpropargyl ethers into the derivatives of 3-oxabicyclo p,3,0]
octane (/2+2+1/ - cycloaddition, Khand-Pauson reac-
tion) is greatly enhanced provided the reaction is carried out in the absence of any solvents with the substrates applied to the surface of SiO2 or A120. This effect has been ascribed to the preferential stabilization of the coiled conformation of the adsorbed acyclic substrate due to the restrictions of its conformational mobility imposed by the interaction with the surface adsorption centers. It has been also suggested' that quite similar effects of the adsorption promotion should be operative in case of other antropy controlled intramolecular reactions. The present study has been undertaken to check the validity of this suggestion for the model example of Carrol reaction2a*b, a variant of /3,3/sigmatropic Claisen rearrangement2csd (Scheme I). Scheme 1
h I According to the conventional procedure Carrol reaction is carried
by a prolonged heating of the acetoacetic ester of ally1 alcohols (as a 4893
4894
neat liquid or in high boiling solvent) at 166-220=~~~~~. Recently the useful alternative to this thermal process has been developped3' involving the transformation of the starting J_under the action of 2 equiv. of LDA in THF3 into bis-enolate, The rearrangement of the latter was found to proceed in refluxing THF giving the respective y,a-unsaturated ketones 2
in good yields.
Our first attempts to carry out transformation 1 -2
on the surface
of the adsorbent met with little success. Thus when acetoacetate of dimewas adsorbed on Si02 (Woelm, 5/4OH
thylvinyl carbinol 3
or florisil (Ser-
va, 40/1OOp) and heated at 600~ for 2-5h, tic data indicated the complete disappearance of 2,
but the analysis of the resulting mixture (after elu-
tion with ether) revealed the presence of only trace amounts of the desired 6-methylhepten-5-on-2 2 cohol 2
the main product being acetoacetate of prenyl al-
isolated in 70% yield'. Thus under these conditions acylotropic
migration took place instead of /3,3/-rearrangement. Scheme 2
Me
Me
‘j”2 l
60’
Me rd0
Me-470de Me
0 la
0 3a
Rather unexpexedly but very rewarding it ha‘sl3eenfound that the use of AI 0 23
instead of Si02 caused a dramatic change in the course of the re-
action and under essentially the same conditions of the thermolysis (60oC, 3h) -la is converted completely into &4
(isolated yield 84%)5,6. Scheme 3
Me
-.
Me
Me0 rP 0
0 la
*$*3 *MeeoMe Me 2a
Acetoacetates of various tertiary ally1 alcohols -lb-e when applied to the surface of A1203 underwent similarly effective Carrol rearrangement leading to the formation of the expected ketones -_ 2b-e in good yields.415 Typical experimental procedure: _'& (l.Og, 4.2 mmol) in hexane (30 ml) was mixed with Al 0 (Woelm, basic, 5/40/J,log), the solvent was removed 23 on a rotovap at 20°C (30 mm Hg) and the resulting powder was heated at 600~ for 5 h (tic control indicated the complete absence of the starting mate-
4895
rial). Elution with hexene, followed by the removal of the solvent and distillation of the residue gave geranylacetone, 3
(0,62g, yield 75%) as a
mixture of E/Z isomers (E:Z=3:2, glc, pmr), b.p. 130-132O (20 mm Hg), I$
b
74-78%
(b) RI= Me, (c) R1 = Me, (d) RI= Me, I c\ Trial(%&%%e~~
lb-e 2b-e R2= Et R2= Me2C=CHCH2 R2= Me2CzCHCH2C(Me)=CHCH2(E) \
fevd$l.%2&t
chromatographic grade Al 0 from va23 riOUS sources (WOelm, FRG; Reanal, Hungary; Chemapol, CSSR; neutral, basic or acidic) differs very little (if any) in transformation 1 _3
its
ability to promote the
2. However the changes in ratio (r) A1203: J_produce
a profound effect on the rate of this conversion. Thus the thermolysis of 2
under standard conditions (600~, 2h) lea to the formation of
(isolated): 75% (;=30), 50%(~=10) and 14% (~=5), the rest being the starting material. It is known that acetoacetic esters of the secondary and especially of the primary ally1 alcohols are less prone to undergo Carrol rearrangement2b and in these cases
the target ketones are formed in modest yields. The at-
tempts to carry out these reactions on Al203 have shown
that: (i) the es-
ters of primary alcohols are not converted into respective ketones after heating at 600~ for 3-6h, while at the elevated temperature (90-IOOO) they are decomposed into the mixture of low boiling hydrocarbons; (II) esters of the secondary alcohols underwent Carrel rearrangement upon the heating in the adsorbed state (on A1203), but the yields of the products me low (e.g. If __L
2f, scheme 5).
Ph
A1203 r@
HO
0
O!f
6a”
rather
Scheme 5
* Phe
Me H
0
45%
2f (E)
Albeit the limitations mentioned the main result of the presented stu-
4896
dy seems to be indisputable: the use of A1203 as a dry media for /3,3/ sigmatropic Carrol rearrangement allows to carry out this reaction at much lower temperatures than those used in classical liquid phase procedure (60-70° instead of 160-220~). This effect seems to be very similar to that observed for the I-
1
rearrangement via bis-enolate induced by the action of the strong base' (vide supra). Hence it was tempting to speculate about a somewhat similar activation of 1 on A1203 due to the presence of Lewis acid and base sites on its surface. However at present we were unable to find any experimental evidence supporting this view'. Hence we prefer the explanation of the phenomena of the rate enhancement of /3,3/ sigmatropic rearrangement on A1203 to be given in the same terms of the adsorption promoted conformational changes of the substrate as had been advanced earlier'. Data presented in this paper taken together with the previous result provide a convincing evidence to the importance of the adsorption as an 8 emerging effective tool for the promotion of the organic reactions and attest to the tremendous potential of the further studies in this field. References 1. S.O.Simonian, W.A.Smit, A.S.Gybin, A.S.Shashkov, G.S.Mikaelian, V.A.Tarasov, I.I.Ibragimov, R.Caple, D.E.Froen, Tetrahedron Lett., 3, 1245 (1986). 2.(a) M.F.Carrol, JOChem.Soc,, 1940, 704; for a review see, (b) L.A.Yanovskaya t'Carro1Reaction", in "Reakzii i methodi issledovaniya organicheskih soedinenii", ~01.12, p.259, Izdatelstvo chimicheskoi literatury, Moscow) 1963; (c) G.B.Bennett, Synthesis 1971, 589; (d) Organic Reactions, vo1.22, p*l. 3. S.R.Wilson, M.F.Price, J.Org.Chem. 49, 722 (1987). 4. All products2rre identified by the comparison with the authentical samples (b.p., nD, glc, PMR); 2b,d,& are formed as E:Z mixtures (3:2). 5. Yields referred to the distilled product. 6. Under classical conditions of Carrol rearrangement could be prepared with the same yield but after heating at 140-160~ for 5h (see for example, W.Kimel, N.N.Sax, S.Kaizer et al., J.Org.Chem., 23, 153 (1958). 7. In this respect it is to be noted, that A1203 pretreated with base (tert.-BuOK or CH30Ha) did not reveal any enhanced activity in the promotion of & 3 conversion. 8. An interesting review covering some aspects of the problem has recently been published by P.Laszlo in Acc.chem.Res. 2, 121 (1986). (Received in UK 29 July 1987)