- Cycloaddition reactions of ketene diethyl acetal toward the synthesis of cyclobutene monomers
-
The [2+2]-cycloaddition reactions of ketene diethyl acetal with methyl acrylate and acrylonitrile were optimized. Highly efficient ketal cleavage to either 2-cyano-1-cyclobutanone or 2-methoxycarbonyl-1-cyclobutanone was achieved using formic acid. Among the numerous reduction methods attempted, only sodium cyanoborohydride in acidic medium led successfully to the corresponding alcohols, but isolation of the desired products was not achievable. We show that the anomalous cyclobutanone chemistry is due to the acidic α-proton and the electron-withdrawing substituent in the α-position. Substitution of the α-proton by a methyl group results in a turnaround back to textbook chemistry. (C) 2000 Elsevier Science Ltd.
- Kniep, Carina S.,Padias, Anne B.,Hall Jr.
-
-
Read Online
- A [2 + 2] Photocycloaddition-Fragmentation Approach toward the Carbon Skeleton of cis-Fused Lycorine-type Alkaloids
-
Starting from isoquinolones, the cis-selective annulation of six-membered rings was possible employing cyclobutenes as olefin components in a [2 + 2] photocycloaddition-fragmentation approach (nine examples, 54-80% yield). The developed sequence enables a
- Wahl, Maike H.,Jandl, Christian,Bach, Thorsten
-
-
Read Online
- Reaction of dimethoxycarbene with strained cyclic carbonyl compounds
-
A cyclopropanone, a cyclopropenone, cyclobutanones, a cyclobutane-1,3-dione, and a cyclobutene-1,2-dione reacted with dimethoxycarbene to afford acetals of the next larger ring by formal insertion of the carbene into a C-C bond α to the carbonyl group. When either of two saturated α-ring carbons could be involved in the process, the ring expansion was selective, affording primarily the product of apparent insertion into the more substituted ring bond. With 2,3-dimethoxycyclobutene-1,2-dione, insertion occurred between the carbonyl groups and with β-propiolactone it occurred at the lactone bond. β-Propiolactam, however, reacted by insertion of the carbene into the N-H bond.
- Venneri,Warkentin
-
p. 1194 - 1203
(2007/10/03)
-