Lewis acid-catalyzed intermolecular [4 + 2] cycloaddition of 3-alkoxycyclobutanones to aldehydes and ketones |
| |
Authors: | Matsuo Jun-ichi Sasaki Shun Tanaka Hiroyuki Ishibashi Hiroyuki |
| |
Institution: | Division of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. jimatsuo@p.kanazawa-u.ac.jp |
| |
Abstract: | Intermolecular 4 + 2] cycloaddition between 3-alkoxycyclobutanones and aldehydes or ketones by the activation with boron trifluoride etherate is reported. The carbonyl compounds are inserted into the less substituted C2-C3 bond of the cyclobutanone ring of 6-alkyl-2-oxabicyclo4.2.0]octan-7-ones to afford 1-alkyl-5,7-dioxabicyclo4.4.0]decan-2-one derivatives regioselectively (>99:1) and diastereoselectively. On the other hand, 4 + 2] cycloaddition of 3-ethoxy-2,2-dialkylcyclobutanones at low temperature proceeds at the more substituted C2-C3 bond to yield 3,3-dialkyl-6-ethoxy-2,3,5,6-tetrahydro-4H-pyran-4-one derivatives with high regioselectivities. This 4 + 2] cycloaddition is developed into a one-pot synthesis of tri- or tetrasubstituted dihydro-gamma-pyrones from 3-ethoxycyclobutanones which are readily prepared from acid chloride and ethyl vinyl ether. The two regioselectivities observed in ring-opening of cyclobutanones can ascribe to thermodynamic stabilities of zwitterionic intermediates generated from tetrahydropyran-fused cyclobutanones and 3-ethoxycyclobutanones. |
| |
Keywords: | |
本文献已被 PubMed 等数据库收录! |
|