Synthesis of functionalized macrocyclic derivatives of trioxabicyclo[3.3.0]nonadiene
作者:Sabine Leber、Gert Kollenz、Curt Wentrup
DOI:10.3762/bjoc.8.83
日期:——
C72-Macrocyclic systems functionalized with nitroaryl and arylamino groups were synthesized from the bisdioxine diacid dichloride 1,3,5,7-tetra-tert-butyl-2,6,9-trioxabicyclo[3.3.1]nona-3,7-diene-4,8-dicarbonyl dichloride (3).
Preparation and Chemistry of an Unexpectedly Stable α-Oxoketene−Pyridine Zwitterion, 2,2-Bis(tert-butylcarbonyl)-1-[4-(dimethylamino)pyridinio]ethen-1-olate
作者:Gert Kollenz、Susanne Holzer、C. Oliver Kappe、Turkaram S. Dalvi、Walter M. F. Fabian、Heinz Sterk、Ming Wah Wong、Curt Wentrup
demonstrate that the ring nitrogen atom of DMAP is involved in generating the new zwitterionic C-N bond. Reactions of 4 with NH and OH nucleophiles in solution afforded the corresponding dipivaloyl acetic acid derivatives 6 and 7, whereas acetone or benzylideneaniline undergo cycloaddition reactions of the hetero-Diels-Alder type.
Dipivaloylketene and its dimers. [2+4] Versus [2+2] cycloaddition reactions of .alpha.-oxo ketenes
作者:C. Oliver Kappe、Gerald Faerber、Curt Wentrup、Gert Kollenz
DOI:10.1021/jo00052a018
日期:1992.12
Dipivaloylketene (8) is generated by preparative flash vacuum pyrolysis of furandione 6. While dimerization of 8 in apolar and several polar solvents leads to the previously reported [2 + 4] dimer 7, dimerization in the presence of DMSO, tributylphosphine oxide, or pyridine instead surprisingly occurs across the C=O bond of the ketene function, affording dioxinone 9. This is a novel type of alpha-oxo ketene dimerization. The reversibility of both dimerizations and mechanistic pathways for the formation of 9 are discussed. Cycloaddition reactions of 8 with heterocumulenes 10a,b and 12a-c yield [2 + 4] cycloadducts 11a,b and 13a-c, respectively. Oxazinones 13a-c can add a second molecule of 8 to generate novel spiro heterocycles 14a-c. In contrast, oxo ketene 7 reacts with carbodiimides 12a,b, to furnish [2 + 2] adducts 15a,b. This is the first unequivocal example of a direct [2 + 2] cycloaddition reaction of an alpha-oxo ketene. The unexpected formation of these compounds was confirmed by X-ray crystallography (15a). General aspects of [2 + 2] versus [2 + 4] cycloaddition in alpha-oxo ketenes are discussed.
Reactions of dipivaloylketene dimer with nucleophiles: new access to the 2,6,9-trioxabicyclo[3.3.1]nona-3,7-diene ring system (bridged bis-dioxines)
作者:C. Oliver Kappe、Gert Kollenz、Walter M. F. Fabian、Curt Wentrup、Gerald Faerber
DOI:10.1021/jo00064a024
日期:1993.6
Novel and convenient methods to prepare several functionalized 2,6,9-trioxabicyclo[3.3.1]nonadienes (''bridged bis-dioxines'') 6, 10, 11, and 12 are described. In general, these are obtained by addition of nucleophiles to alpha-oxoketene 5 in a multistep reaction sequence, where the specific reaction pathway depends strongly on the type of nucleophile employed: Aromatic amines with electron-donating substituents afford the trioxabicyclononadienes 6, while with aliphatic amines or thiolates, 2 equiv of the corresponding dipivaloylacetamides 13 or thioesters 14, respectively, are formed. In the case of OH nucleophiles, the primary 1:1 adducts 8 are isolable, characterized by an X-ray analysis of 8a. Under acidic conditions, 8 can be cyclized to the bifunctionalized bis-dioxines 10. The bis-carboxylic acid 10c serves as a valuable intermediate to synthesize other derivatives, e.g. the bis-acid chloride 11 and the bis-ester 12. Mechanistic pathways leading to the various reaction products are discussed in detail and supported by semiempirical molecular orbital calculations using the AM1 method. The spontaneous formation of the bis-dioxine skeleton in the reaction 5 --> 6 is likely to proceed via an unusual [4 + 4] type tandem cyclization reaction.
Kappe, C. Oliver; Evans, Richard A.; Kennard, Colin H. L., Journal of the American Chemical Society, 1991, vol. 113, # 11, p. 4234 - 4237
作者:Kappe, C. Oliver、Evans, Richard A.、Kennard, Colin H. L.、Wentrup, Curt