Different Reactivity Patterns of Trimethylsilyl- and Phenyl-Substituted Propargylallenes: Fe₂(CO)₉- and [Ag]⁺-Promoted Cyclizations

Abstract

Thermolytic rearrangement of the diphenyl-propargylallene [3,3-(biphenyl-2,2′-diyl)-1-phenyl-1-{9-[(phenylethynyl]-9H-fluorenyl}allene], 9, yields the bis-fluorenyliden-bis-allene 10, which undergoes electrocyclization to form 3,4-di(fluorenyliden)-1,2-diphenylcyclobutene, 12, in which the overlapping fluorenylidenes give rise to C2 symmetry. The propargylallene 9 reacts with iron carbonyls to form 15, in which an (η5-fluorenyl)Fe(CO)2 moiety is linked both directly and via a bridging ═C(Ph)−C(═O)− linkage to a cyclobutene ring possessing a phenyl group and a spiro-bonded fluorenyl substituent. The diphenyl-propargylallene 9 and its bis(trimethylsilyl)propargylallene analogue, 2, each react with Co2(CO)8 to furnish the corresponding alkyne-Co2(CO)6 complexes 14 and 13, respectively. Treatment of the diphenyl-propargylallene 9 or the mono(trimethylsilyl)propargylallene 25 with silver nitrate in methanol or water effects cyclization of the allene onto the alkyne to furnish a cyclopentadiene that bears a 9-methoxy- or 9-hydroxy-fluorenyl substituent and is also spiro-bonded to a second fluorenyl moiety. The reaction of 3,3-(biphenyl-2,2′-diyl)-1-bromo-1-phenylallene with Fe2(CO)9 yields the novel bicyclo[3.2.0]heptadienone 21, which possesses two phenyl groups and is also spiro-linked to two fluorenyl fragments. All new compounds were characterized by NMR spectroscopy and X-ray crystallography.