Date of Graduation
Eberly College of Arts and Sciences
Kung K. Wang.
The cascade radical cyclization of benzannulated enyne-allene generated in situ from enediynyl propargylic alcohols promoted by thionyl chloride via an SNi' reaction provides an efficient synthetic pathway to 11H-benzo[b]fluoren-11-ols and related compounds. The simplicity of the synthetic sequence and the mildness of the reaction condition make this cascade reaction sequence useful for the construction of polycyclic aromatic compounds. Interestingly, when this strategy was employed for the systems having two benzannulated enyne-allene units, it was quite unexpected that the reaction sequence led to the formation of highly twisted 1,1'-dialkyl-9,9'-bifluorenylidenes involving an unusual cleavage of a benzene ring, and spiro[1H-cyclobut[ a]indene-1,9'-[9H]fluorenes] along with other polycyclic aromatic compounds. Conceivably, the transformation from the precursors having two benzannulated enyne-allene units to the novel polycyclic compounds involves a C2-C6 cyclization reaction followed by a radical-radical coupling reaction and a tautomerization to give the formal Diels-Alder adducts or the [2+2] cycloaddition adducts.;The Ireland-Claisen rearrangement of the benzannulated enediynyl propargylic acetates was successfully adopted for the synthesis of the corresponding benzannulated enyne-allenes in situ for the subsequent Schmittel cyclization to generate benzofulvene biradicals for cascade radical cyclizations. The mildness of the reaction conditions and the ready availability of a variety of silyl ketene acetal make this synthetic pathway quite attractive. Several polycyclic aromatic derivatives of benzo[ghi]fluoranthene and 11H-benzo[ b]fluorene were thus produced from the corresponding enediynyl propargylic acetates in a single operation.;The Wagner-Meerwein rearrangement of fluorenylmethanols derived from 15,16-diaryl-diindeno[2,1-b:1',2 '-h]phenanthrenes was successfully adopted for the synthesis of helical 17,18-diaryl-dibenzo[a,o]pentaphenes involving the carbocation-promoted ring expansion and aromatization. Two of the 17,18-diaryl-dibenzo[a,o]pentaphenes were employed for the subsequent intramolecular Friedel-Crafts arylation reactions involving phenyl or 4-biphenylyl substiuents at the 17 & 18 positions, producing several butterfly-shaped compounds having two planes of symmetry and a C2 symmetry in the case of the phenyl substituent and having only a C2 symmetry in the case of the 4-biphenylyl substituent. They possess very interesting structural features.
Yang, Yonghong, "Cascade radical cyclizations of benzannulated enyne-allenes and development of new synthetic strategies for novel polycyclic aromatic compounds" (2004). Graduate Theses, Dissertations, and Problem Reports. 2097.