Thermal rearrangements in the tetra-arylcyclopropene series

Abstract

THE literature provides many examples of thermal rearrangements of small-ring compounds to yield systems involving less bond-angle strain.' In the arylcyclopropene series these involve, in many cases, fairly complex pathways, and only formalized mechanisms have been suggested .l,2 Tetra-arylcyclopropenes have the advantage of no labile hydrogen atom, exhibit moderate thermal stability, and would be expected to yield only primary products from ring cleavage. We now report that 3-aryl-l,2,3-triphenylcyclopropenes (I) readily available by action of the appropriate aryl Grignard reagent on triphenylcyclopropenyl bromide, rearrange, either in a melt above 200" or in solution at somewhat lower temperatures, to 1,2,3-triarylindenes. The rearrangement also proceeds under acidic conditions at considerably lower temperature.8Molten tetraphenylcyclopropene (Ia)* rearranged at 235-240" in almost quantitative yield to 1,2,3-triphenylindene (IIa) The rearrangement exhibited first-order kinetics in diphenyl ether (88%)-quinoline (12%) (See Table), but was sensitive to traces of acid and oxygen.?7 Analysis was by n.m.r. integration, a t 120°, of the increasing 1-indenyl proton (T 4.93) against the aliphatic protons Erratic mm. Hg, and with less than 12% quinoSince (IIa), as well as most triarylindenes, fluoresces strongly in the visible the rearrangeof fluorene (7 6-28) used as an internal standard. kinetic behaviour was observed for tubes sealed a t pressures greater than line in the solvent mixture. ment can also be conveniently followed by fluorimetry.The average of 12 integrations was taken for each point.

Reactivity of phenyliodonium bis(arylsulphonyl)methylides towards alkenes and alkynes: crystal structure of 9-phenylsulphonyl-1,2,3,4,4a,9a-hexahydro-1,4- methanofluorene

“…We find that the gem-disulphones [(4b (8); Table 13 are somewhat labile, since extensive decomposition occurred upon storage for 2 months at room temperature. A dramatic manifestation of this instability was provided by the reaction of (3) with norbornene, where the only isolable product after the reaction had been stirred at room temperature for 6 days was the indane monosulphone (9) in high yield, whose structure has been confirmed by an X-ray analysis.…”

“…Compound (3) was refluxed in chloroform (10 ml) containing cis,cis-cyclo-octa-1,5-diene (3 ml) with Cu(acac), (1 mg) in N, for 75 min. The residue after removal of volatiles was chromatographed to give some hydrocarbon and phenyl benzenethiosulphonate and then compound(8) in 37% yield, m.p. 193-195 "C (from chloroform-hexane); vmax.Phenylsulphonyl-1,2,3,4,4a,9a-hexahydro-1,4-methano-,fluorene (9).--Compound (3) was stirred in methylene dichloride (10 ml) and norbornene (0.7 g) under N, for 6 days.…”

Generation and Trapping of Cyclopropenes from 2‐Alkoxy‐1,1‐dichlorocyclopropanes

“…The pyrolysis of 15 [27] at 250" during 10 min afforded 3-methoxy-l,2-diphenyl-l H-indene (16; 70 %), 2,3-dihydro-2,3-diphenyl-l H-inden-lone (17; 12 %), and l-methoxy-2,3-dipheny1-1 H-indene (18; 5 %) [28], all products derived from vinylcarbene 19b, but no products originating from the thermodynamically 15 has to be heated at 230°, which corresponds to the temperature at which tetraphenylcyclopropene rearranges. Other authors [30] [3 11 have noted that the presence of a MeS substituent at C( 1) of the cyclopropene greatly facilitates carbene formation, while substitution by MeS or Ph [26] at C(3) has no effect. This is consistent with the observation, that I-chlorocyclopropenes rearrange to chlorovinyl carbenes at room or sub-room temperatures [5], while their counterparts lacking the carbene-stabilizing C1-substituent do not ring open at low temperature.…”

“…Vinylcarbenes, generated from diazo compounds with Rh,(OAc),, react with furans generally by (formal) [3 + 41 cycloaddition [25]. So far, only a few vinylcarbenes derived from cyclopropenes have been trapped by intramolecular insertion reactions [26]. Moreover, these reactions often were mechanistically poorly analyzed.…”

Reaktionen von Komplexliganden, XVI. Synthese von Inden‐Derivaten aus Carben‐Komplexen und Alkinen

“…Kristalldaten: C24H22O ( (4) 0.2971 (5) 0.3593 (5) 0.471 2(5) 0.5612 (5) 0.6609 (5) 0.6635 (5) 0.4144 (5) 0.2198 (4) 0.7021 (5) 0.2321 (5) 0.1401 (5) C.1152 (5) O.lOSS (5) 0.4228 (5) 0.5113 (5) 0 . i a37 (5) 0.1 lW (5) 0.0067 ( 6 ) 0.0315 (5) 0.1414 (5) 0.5131 (5) 0.3313 (3) 0.2435 (6) -n.o337 (5) 0.0551 (4) C.1194 (4) 0.2316 (4) 0.1554 (5) 0.1140 (5) 0.0810(5) -0.0237 (5) -0.0416 (5) 0.0500 (4) -O.C625 (4) -0.1142 (5) -0.2834 ( 5) -0.2833 (5) -0.1723 (5) -0.0634(4) 0.0652 (5) 0.2289 (4) 0.1534 (5) 0.1995 (5) 0.3224 (5) 0.3981 (5) 0.3546 <...>…”