- Reaction of dimethoxycarbene with strained cyclic carbonyl compounds
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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
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p. 1194 - 1203
(2007/10/03)
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- Cyclopropyl building blocks for organic synthesis, 36: Unprecedented addition of dialkoxycarbenes to tetrasubstituted alkenes: Bicyclopropylidene and 2-chlorocyclopropylideneacetate
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The cycloaddition reactions of several dialkoxycarbenes generated in situ from the corresponding 2,2-dialkoxy-Δ3-1,3,4-oxadiazolines of the type 3 with bicyclopropylidene 1 afford the dialkyl acetals of dispiro[2.0.2.1]heptane-7-one (4), whereas the analogous addition to methyl (1-chloromethylene-1-carboxylate)cyclopropane 26 leads to the formation of a complex mixture of products. Those products can best be rationalized in terms of nucleophilic attack of the dialkoxycarbene on the strained CC double bond, to form a dipolar intermediate capable of a variety of intramolecular rearrangements. Several chemical transformations of the compounds of type 4 are reported. VCH Verlagsgesellschaft mbH, 1996.
- De Meijere, Armin,Kozhushkov, Sergei I.,Yufit, Dmitry S.,Boese, Roland,Haumann, Thomas,Pole, David L.,Sharma, Pradeep K.,Warkentin, John
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p. 601 - 612
(2007/10/03)
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- Carbon-Oxygen Bond Insertion in the Reaction of Dialkoxycarbenes with Anhydrides
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Dimethoxycarbene (1a) and methoxy(2,2,2-trifluoroethoxy)carbene (1b) were generated in benzene solution by thermolysis of the corresponding 2,2-dialkoxyoxadiazolines 7.The carbenes were trapped by intermolecular reaction with a variety of cyclic anhydrides 8.The products 9 are formally the result of carbene insertion into the bond between the carbonyl carbon and the ring oxygen atoms.The results of a competition between dimethylmaleic and dichloromaleic anhydrides for dimethoxycarbene suggests that this reaction proceeds by nucleophilic attack of dialkoxycarbene onto the carbonyl carbon atom of the anhydride. - Keywords: Carbenes, dialkoxy-; Oxadiazolines; C-O insertion; Carbonyl additions; Anhydrides
- Pole, David L.,Warkentin, John
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p. 1907 - 1914
(2007/10/03)
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- Electrooxidative Cyclization of N-Acylhydrazones of Aldehydes and Ketones to Δ3-1,3,4-Oxadiazolines and 1,3,4-Oxadiazoles
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The electrolytic oxidation of ketone N-acylhydrazones (1) in methanolic sodium acetate induced their intramolecular cyclization to the corresponding 2-methoxy-Δ3-1,3,4-oxadiazolines 3.The thermal stability of a given oxadiazoline and what products were formed by its thermal decomposition was found to depend on the natures of the substituents at C-2.Thus, 2-methoxy-2-phenyloxadiazolines preferentially yielded oxiranes 5, whereas 2-alkyl-2-methoxyoxadiazolines preferentially gave enol ethers 6. 2,2-Dimethoxyoxadiazolines decomposed to the parent ketones and many unidentified products.The electrolytic oxidation of aldehyde N-acylhydrazones 2 gave 2,5-disubstituted 1,3,4-oxadiazoles 4.The oxidative cyclization of the N-benzoylhydrazones of aliphatic aldehydes gave especially high yields of the corresponding heterocycles.
- Chiba, Toshiro,Okimoto, Mitsuhiro
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p. 1375 - 1379
(2007/10/02)
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