Details
| Original language | English |
|---|---|
| Pages (from-to) | 1972-1983 |
| Number of pages | 12 |
| Journal | European Journal of Organic Chemistry |
| Issue number | 12 |
| Publication status | Published - 2002 |
Abstract
Tricarbonyl(3-methoxybenzocyclobutenedione) chromium (rac-3) has a lower symmetry than the corresponding unsubstituted benzocyclobutenedione complex. This has consequences for reaction sequences involving both ketone functionalities. The relative electrophilicity of the two ketone functions was evaluated by partial reduction of rac-3 and by a partial hydrolysis of the bis(ethylene acetal), the precursor of rac-3. In addition, monovinyl Grignard addition was performed. All three experiments indicated a higher electrophilicity of C-1 than of C-2, in agreement with the resonance formulas that can be drawn. Dianionic oxy-Cope rearrangements, followed by intramolecular aldol addition, occurred with remarkable regioselectivity: in five of six cases investigated only one of two expected reaction products was obtained. As an explanation of this remarkable selectivity we considered a chelation effect of the intermediate bis(enolate) involving the 3-methoxy substituent. This causes a rare, if not the first, case of differentiation of two enolate moieties present in the cyclooctane ring. Addition of 2-lithio-3,4-dihydro-2H-pyran did not give rise to a dianionic oxy-Cope rearrangement but instead to a rare example of an anionic 1-vinylcyclobutenol-cyclohexadienol rearrangement. Five compounds presented in this publication have been characterized by crystal structure analyses.
Keywords
- Aldol reaction, Chromium, Nucleophilic addition, Rearrangement, Ring-expansion
ASJC Scopus subject areas
- Chemistry(all)
- Physical and Theoretical Chemistry
- Chemistry(all)
- Organic Chemistry
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In: European Journal of Organic Chemistry, No. 12, 2002, p. 1972-1983.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Tricarbonyl(3-methoxybenzocyclobutenedione)chromium
T2 - Regioselective nucleophilic addition reactions, dianionic oxy-cope rearrangements, regioselective intramolecular aldol additions, and a rare case of an anionic 1-vinylcyclobutenol-cyclohexadienol rearrangement
AU - Dongol, Krishna Gopal
AU - Wartchow, Rudolf
AU - Butenschön, Holger
PY - 2002
Y1 - 2002
N2 - Tricarbonyl(3-methoxybenzocyclobutenedione) chromium (rac-3) has a lower symmetry than the corresponding unsubstituted benzocyclobutenedione complex. This has consequences for reaction sequences involving both ketone functionalities. The relative electrophilicity of the two ketone functions was evaluated by partial reduction of rac-3 and by a partial hydrolysis of the bis(ethylene acetal), the precursor of rac-3. In addition, monovinyl Grignard addition was performed. All three experiments indicated a higher electrophilicity of C-1 than of C-2, in agreement with the resonance formulas that can be drawn. Dianionic oxy-Cope rearrangements, followed by intramolecular aldol addition, occurred with remarkable regioselectivity: in five of six cases investigated only one of two expected reaction products was obtained. As an explanation of this remarkable selectivity we considered a chelation effect of the intermediate bis(enolate) involving the 3-methoxy substituent. This causes a rare, if not the first, case of differentiation of two enolate moieties present in the cyclooctane ring. Addition of 2-lithio-3,4-dihydro-2H-pyran did not give rise to a dianionic oxy-Cope rearrangement but instead to a rare example of an anionic 1-vinylcyclobutenol-cyclohexadienol rearrangement. Five compounds presented in this publication have been characterized by crystal structure analyses.
AB - Tricarbonyl(3-methoxybenzocyclobutenedione) chromium (rac-3) has a lower symmetry than the corresponding unsubstituted benzocyclobutenedione complex. This has consequences for reaction sequences involving both ketone functionalities. The relative electrophilicity of the two ketone functions was evaluated by partial reduction of rac-3 and by a partial hydrolysis of the bis(ethylene acetal), the precursor of rac-3. In addition, monovinyl Grignard addition was performed. All three experiments indicated a higher electrophilicity of C-1 than of C-2, in agreement with the resonance formulas that can be drawn. Dianionic oxy-Cope rearrangements, followed by intramolecular aldol addition, occurred with remarkable regioselectivity: in five of six cases investigated only one of two expected reaction products was obtained. As an explanation of this remarkable selectivity we considered a chelation effect of the intermediate bis(enolate) involving the 3-methoxy substituent. This causes a rare, if not the first, case of differentiation of two enolate moieties present in the cyclooctane ring. Addition of 2-lithio-3,4-dihydro-2H-pyran did not give rise to a dianionic oxy-Cope rearrangement but instead to a rare example of an anionic 1-vinylcyclobutenol-cyclohexadienol rearrangement. Five compounds presented in this publication have been characterized by crystal structure analyses.
KW - Aldol reaction
KW - Chromium
KW - Nucleophilic addition
KW - Rearrangement
KW - Ring-expansion
UR - http://www.scopus.com/inward/record.url?scp=0036080969&partnerID=8YFLogxK
U2 - 10.1002/1099-0690(200206)2002:12<1972::AID-EJOC1972>3.0.CO;2-H
DO - 10.1002/1099-0690(200206)2002:12<1972::AID-EJOC1972>3.0.CO;2-H
M3 - Article
AN - SCOPUS:0036080969
SP - 1972
EP - 1983
JO - European Journal of Organic Chemistry
JF - European Journal of Organic Chemistry
SN - 1434-193X
IS - 12
ER -