Udo H. Brinker

First formation of 1,1-dihalo-1,3-butadienes from reactions of dichloro- and dibromocarbenes with cyclopropenes via new addition-rearrangements

Abstract New dichloro- and dibromocarbene addition-rearrangements are reported. In the reactions of 1,2-diarylcyclopropenes with difluoro-, dichloro-, dibromo-, and bromofluorocarbene, 2,3-diaryl-1,1-dihalo-1,3-butadienes are formed. In addition, 1,3-diaryl-2,3-dihalocyclo-1-butenes are formed. For the formation of the 1,1-dihalobutadienes, new addition-rearrangement mechanisms are proposed. Furthermore, some reactions of cyclobutenes with dihalocarbenes are described.

Carbenes in constrained systems. 4. Encapsulation of an asymmetric diazirine: Reactivity of 2-methylcyclohexanylidene

Abstract 2-Methylcyclohexanylidene was generated from the corresponding diazirine within the cavities of α-, β- and γ-cyclodextrin by photolysis in the solid state. To surmise how these constrained systems affect the residing carbenes selectivity, a comparison with conventional reaction methods was made.

Synthesis of a sterically congested diazirine: 2-azi-camphane

Abstract The synthesis of 2-azi-camphane has been achieved despite the fact that the spirocyclic carbon center is sterically congested. Although the yield is somewhat low, the highly pure diazirine can be used as a precursor for the burgeoning class of sterically congested carbenes.

Competing 1,n-elimination reactions of 1-Bromo-5-bromomethyl-6,6-dichlorobicyclo[3.1.0]hexane: A strained 1,3-bridged cyclopropene and a vinylcarbene as reactive intermediates☆

Abstract 1-Bromo-5-bromomethyl-6,6-dichlorobicyclo[3.1.0]hexane (9) was treated with alkyllithium at different temperatures. After halogen metal exchange in 9, two competing 1,n-elimination reactions take place. A 1,2-elimination of organolithium compound 12 leads to strained 1,3-bridged cyclopropene 10 which undergoes a cyclopropene-vinylcarbene rearrangement to 17. Insertion of 17 into the ether solvent affords isomers 18a and 18b. In contrast, 1,4-eliminations of organolithium compound 13 generate butadienes 14 and 16, respectively. The formation of the products is temperature dependent.

A new mechanism for reactions of carbenes and bicyclo[1.1.0]butanes☆

Abstract Reactions of tricyclo[4.1.0.02,7]heptane (1) with dihalocarbenes and bromine are reported. A new side bond opening mechanism for reactions of carbenes and bicyclo[1.1.0]butanes is proposed.