Date of Award

Spring 1998

Abstract

I. The synthesis, trapping, and strain energy estimates for cyclic butatrienes are described. Four fundamental questions have been investigated: kinetic stability limitations, molecular strain, structural limitations, and the development of a general synthetic route applicable to different ring sizes.

1,2,3-Cyclooctatriene (9) has been generated by magnesium induced 1,2-elimination on 2-bromo-3-chloro-1,3-cyclooctadiene (4). Synthesis of the eight-membered ring completes the C$\sb6$-C$\sb{10}$ series of cyclic butatrienes. This substance shows moderate kinetic stability, but is readily trapped in a ($\rm\sb\pi2\sb{s}{+}\sb\pi4\sb{s}\rbrack$ cycloaddition with diphenylisobenzofuran or 2,5-dimethylfuran. The total strain energy and the strain in the butatriene moiety in cumulene 9 have been assessed by ab initio calculations. The estimates are 17.7 kcal/mol and 12.4 kcal/mol, respectively, at the MP2/6-31G*//HF/3-21G level.

1,2,3-Cycloheptatriene (0) and its isomer cyclohepten-3-yne (9) are readily accessible by magnesium induced 1,2-elimination on appropriate precursors. The calculated total strain energy in the cyclic butatriene, and in the seven-membered enyne are 31.8 kcal/mol and 30.8 kcal/mol, respectively, at the MP2/6-31G*//HF/3-21G level.

5,5-Dimethyl-1,2,3-cyclopentatriene (5) remains elusive. Five likely precursors have been prepared and studied; no evidence for the existence of this compound was found.

Intramolecular vinylidene coupling has been explored as a possible ring-size-independent synthetic route to cyclic butatrienes. In the cases of tetrabromo-olefins 22 and 27 a 1,2-migration occurs faster than the ring closure which would give the cumulene.

II. A general route to cleanly photogenerate reactive carbenes by photolysis of cyclopropanated phenanthrenes has been studied. The adduct of dichlorocarbene and phenanthrene has been modified to produce shelf-stable substances that serve as photochemical precursors to vinylcarbene, and acyclic and cyclic vinylidenes.

Low temperature irradiation of 7-endo-ethylenedibenzo (a;b) bicyclo (4.10) heptane (41) at 254 nm cleanly gives phenanthrene (35) and vinylcarbene (36); the latter rapidly rearranges to cyclopropene. The strained alkene is efficiently trapped by cycloadditions with cyclopentadiene or diphenylisobenzofuran.

Fragmentation of a C$\sb9$ vinylidene precursor 58 leads to efficient formation of 1-nonyne (60) by 1,2-shift.

Cyclobutylidenecarbene (63) rearranges readily to cyclopentyne (3). Cycloalkyne 3 is trapped by cyclohexene to give tricyclo (6.3.0.0$\sp{2,7}\rbrack$undec-1(8)-ene (68) and a cyclohexyl derivative 72 which has not been previously described.

Rearrangements of cyclopentylidenecarbene (63) and cyclohexylidenecarbene (64) are not observed. These carbenes are trapped in (2+1) cycloadditions with cyclohexene.

Document Type

Dissertation

Department or Program

Chemistry

Degree Name

Doctor of Philosophy

Download

Share

COinS