Details
| Original language | English |
|---|---|
| Pages (from-to) | 1167-1173 |
| Number of pages | 7 |
| Journal | Liebigs Annalen |
| Issue number | 7 |
| Publication status | Published - Jul 1996 |
Abstract
The chemistry of the highly substituted cyclobutanone derivative 2, which is easily accessible from 1, is dominated by the steric hindrance caused by the substituents: Reduction with hydride reagents and nucleophilic additions with methyllithium are less stereoselective than corresponding reactions with less substituted bicyclo[3.2.0]hept-2-en-6-one derivatives, but under certain conditions, the exo product predominates. With methyl-, benzyl-, ethenyl-, and ethynylmagnesium halides no nucleophilic addition at the carbonyl group is observed, presumably as a result of the steric hindrance. Instead, an unexpected rearrangement to the bicyclo[4.1.0]heptane carbon skeleton occurs with complete diastereoselectivity and high yields. The rearrangement is rationalized by an increase of the carbocationic character of the carbonyl carbon atom as a result of a coordination of the carbonyl oxygen atom at the Lewis acidic magnesium. This facilitates rearrangement of a cyclobutyl carbenium ion to a cyclopropylmethyl carbenium ion, the latter being stabilized by the amino group. Remarkably, with Grignard reagents derived from propargyl or allyl halides, no rearrangement is observed. The constitutions and configurations of the products were determined by 1H- and 13C-NMR spectroscopy using techniques including NOESY and 2D-INADEQUATE.
Keywords
- Bicyclo[3.2.0]hept-2-en-6-one, Bicyclo[4.1.0]hept-4-en-1-ol, Rearrangements
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In: Liebigs Annalen, No. 7, 07.1996, p. 1167-1173.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Rearrangement of a Bicyclo[3.2.0]hept-2-ene to a Bicyclo[4.1.0]hept-4-ene
AU - Behrendt, Uwe
AU - Gabor, Barbara
AU - Mynott, Richard
AU - Butenschön, Holger
PY - 1996/7
Y1 - 1996/7
N2 - The chemistry of the highly substituted cyclobutanone derivative 2, which is easily accessible from 1, is dominated by the steric hindrance caused by the substituents: Reduction with hydride reagents and nucleophilic additions with methyllithium are less stereoselective than corresponding reactions with less substituted bicyclo[3.2.0]hept-2-en-6-one derivatives, but under certain conditions, the exo product predominates. With methyl-, benzyl-, ethenyl-, and ethynylmagnesium halides no nucleophilic addition at the carbonyl group is observed, presumably as a result of the steric hindrance. Instead, an unexpected rearrangement to the bicyclo[4.1.0]heptane carbon skeleton occurs with complete diastereoselectivity and high yields. The rearrangement is rationalized by an increase of the carbocationic character of the carbonyl carbon atom as a result of a coordination of the carbonyl oxygen atom at the Lewis acidic magnesium. This facilitates rearrangement of a cyclobutyl carbenium ion to a cyclopropylmethyl carbenium ion, the latter being stabilized by the amino group. Remarkably, with Grignard reagents derived from propargyl or allyl halides, no rearrangement is observed. The constitutions and configurations of the products were determined by 1H- and 13C-NMR spectroscopy using techniques including NOESY and 2D-INADEQUATE.
AB - The chemistry of the highly substituted cyclobutanone derivative 2, which is easily accessible from 1, is dominated by the steric hindrance caused by the substituents: Reduction with hydride reagents and nucleophilic additions with methyllithium are less stereoselective than corresponding reactions with less substituted bicyclo[3.2.0]hept-2-en-6-one derivatives, but under certain conditions, the exo product predominates. With methyl-, benzyl-, ethenyl-, and ethynylmagnesium halides no nucleophilic addition at the carbonyl group is observed, presumably as a result of the steric hindrance. Instead, an unexpected rearrangement to the bicyclo[4.1.0]heptane carbon skeleton occurs with complete diastereoselectivity and high yields. The rearrangement is rationalized by an increase of the carbocationic character of the carbonyl carbon atom as a result of a coordination of the carbonyl oxygen atom at the Lewis acidic magnesium. This facilitates rearrangement of a cyclobutyl carbenium ion to a cyclopropylmethyl carbenium ion, the latter being stabilized by the amino group. Remarkably, with Grignard reagents derived from propargyl or allyl halides, no rearrangement is observed. The constitutions and configurations of the products were determined by 1H- and 13C-NMR spectroscopy using techniques including NOESY and 2D-INADEQUATE.
KW - Bicyclo[3.2.0]hept-2-en-6-one
KW - Bicyclo[4.1.0]hept-4-en-1-ol
KW - Rearrangements
UR - http://www.scopus.com/inward/record.url?scp=0344486809&partnerID=8YFLogxK
U2 - 10.1002/jlac.199619960716
DO - 10.1002/jlac.199619960716
M3 - Article
AN - SCOPUS:0344486809
SP - 1167
EP - 1173
JO - Liebigs Annalen
JF - Liebigs Annalen
SN - 0365-5490
IS - 7
ER -