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Stereoselective synthesis of tricyclic compounds by intramolecular palladium-catalyzed addition of aryl iodides to carbonyl groups

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ABSTRACT

Starting from γ-ketoesters with an o-iodobenzyl group we studied a palladium-catalyzed cyclization process that stereoselectively led to bi- and tricyclic compounds in moderate to excellent yields. Four X-ray crystal structure analyses unequivocally defined the structure of crucial cyclization products. The relative configuration of the precursor compounds is essentially transferred to that of the products and the formed hydroxy group in the newly generated cyclohexane ring is consistently in trans-arrangement with respect to the methoxycarbonyl group. A transition-state model is proposed to explain the observed stereochemical outcome. This palladium-catalyzed Barbier-type reaction requires a reduction of palladium(II) back to palladium(0) which is apparently achieved by the present triethylamine.

No MeSH data available.


Molecular structure (ORTEP [14]) of compound 15b (thermal ellipsoids at 50% probability).
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Figure 4: Molecular structure (ORTEP [14]) of compound 15b (thermal ellipsoids at 50% probability).

Mentions: With cycloheptanone derivatives 5a/b less efficient cyclizations were observed. The mixture of diastereomers 5a/5b (ca. 1:1) provided a mixture of compounds containing the two isomers 15a and 15b, from which pure 15a could be isolated (Scheme 6). A diastereomerically enriched sample of 5b afforded compound 15b in 45% yield as a single isomer. These results were obtained employing microwave irradiation (400 W) that allowed considerably shorter reaction times, however, the yields were not strongly influenced by this modification. From both product diastereomers crystals suitable for X-ray crystal structure analyses could be obtained (Fig. 3 and Fig. 4) [16–17]. Again, the configurations of the precursors are reflected in the product structure. Compound 5b provided product 15b with trans-annulation of the two rings and we assume that compound 15a with cis-annulated rings was formed selectively from precursor 5a.


Stereoselective synthesis of tricyclic compounds by intramolecular palladium-catalyzed addition of aryl iodides to carbonyl groups
Molecular structure (ORTEP [14]) of compound 15b (thermal ellipsoids at 50% probability).
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979759&req=5

Figure 4: Molecular structure (ORTEP [14]) of compound 15b (thermal ellipsoids at 50% probability).
Mentions: With cycloheptanone derivatives 5a/b less efficient cyclizations were observed. The mixture of diastereomers 5a/5b (ca. 1:1) provided a mixture of compounds containing the two isomers 15a and 15b, from which pure 15a could be isolated (Scheme 6). A diastereomerically enriched sample of 5b afforded compound 15b in 45% yield as a single isomer. These results were obtained employing microwave irradiation (400 W) that allowed considerably shorter reaction times, however, the yields were not strongly influenced by this modification. From both product diastereomers crystals suitable for X-ray crystal structure analyses could be obtained (Fig. 3 and Fig. 4) [16–17]. Again, the configurations of the precursors are reflected in the product structure. Compound 5b provided product 15b with trans-annulation of the two rings and we assume that compound 15a with cis-annulated rings was formed selectively from precursor 5a.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Starting from γ-ketoesters with an o-iodobenzyl group we studied a palladium-catalyzed cyclization process that stereoselectively led to bi- and tricyclic compounds in moderate to excellent yields. Four X-ray crystal structure analyses unequivocally defined the structure of crucial cyclization products. The relative configuration of the precursor compounds is essentially transferred to that of the products and the formed hydroxy group in the newly generated cyclohexane ring is consistently in trans-arrangement with respect to the methoxycarbonyl group. A transition-state model is proposed to explain the observed stereochemical outcome. This palladium-catalyzed Barbier-type reaction requires a reduction of palladium(II) back to palladium(0) which is apparently achieved by the present triethylamine.

No MeSH data available.