Ketenes. III. Cycloaddition of Ketenes to Acetylenic Ethers¹

Abstract

Dialkylketenes add to ethoxyacetylene to give 4,4-dialkyl-3-ethoxy-2-cyclobuten-l-ones and to l-buten-3-ynyl methyl ether to give 4,4-dialkyl-3-(2-methoxyvinyl)-2-cyclobuten-l-ones. Some new reactions of these cyclobutenones are described.

Bromo-Cyclobutenaminones as New Covalent UDP-N-Acetylglucosamine Enolpyruvyl Transferase (MurA) Inhibitors

“…The two methyl groups were incorporated so as to restrict the nucleophilic character of enaminones (14a-e) to but one position in, e.g., the electrophilic bromination. The sequence furnished ethoxyenone (12) in moderate yield, which was transformed by acidic hydrolysis to 2,2-dimethylcyclobutane-1,3-dione (13) in high yield [18][19][20][21]. Next, dione 13 was condensed with various amines in the presence of AcOH as catalyst at 65 °C to generate the desired enaminones (14a-e) in moderate yields [18,22].…”

“…The synthesis of a small set of cyclobutenaminones was accomplished using a strategy based on that from Brand et al (Scheme 1) [18]. The sequence began with ethoxyacetylene (11), which underwent a [2+2] cycloaddition [18][19][20][21] with the in situ generated ketene formed via the base-mediated HCl elimination from isobutyryl chloride. The two methyl groups were incorporated so as to restrict the nucleophilic character of enaminones (14a-e) to but one position in, e.g., the electrophilic bromination.…”

Ketene Recognizes 1,3-Dienes in Their s-Cis Forms through [4 + 2] (Diels−Alder) and [2 + 2] (Staudinger) Reactions. An Innovation of Ketene Chemistry

“…The rate preference of 2 to cyclopentene has been explained by the secondary orbital interaction in TS( C ) of Scheme . 12e,15b But, Staudinger reactions of open-chain 1,3-dienes were found to be considerably slower than those of cyclic 1,3-dienes . Introduction of an electron-donating substituent, methoxy group, at the 1-position of open-chain 1,3-butadiene increases the reactivity of the diene . It is curious that the ethylene bond is more reactive than the vinyl ether double bond of the diene in this reaction.…”

“…Scheme illustrates the exceptions, i.e., the reactions of ketenes with conjugated dienes giving 1,4-cycloadducts or via [4 + 2] cycloadditions. The first symptom of the 1,4-addition of a ketene toward a diene was reported in 1965 (Scheme a). , An electron-deficient bis(trifluoromethyl)ketene reacts with butadiene to form a 1,4-cycloadduct across the CO bond of ketene (Scheme b) are obtained exceptionally (Scheme c) in the mixture of [4 + 2] and [2 + 2] cycloadducts .…”

Utilizing the high dielectric constant of water: efficient synthesis of amino acid-derivatized cyclobutenones

“…[29][30][31] Examining this substitution reaction in different solvents reveals that this substitution reaction indeed does not proceed well in organic solvents (Table 1). 32,33 Substitution reaction of cyclobutenone 2 with L-serine shows that the rate in DMSO-d 6 (5 Â 10 À5 L mol À1 s À1 ) is slightly higher than that in CD 3 OD (3.5 Â 10 À5 L mol À1 s À1 ).…”