Free Radical Rearrangements in the Decarbonylation of Aldehydes¹

Abstract

The reaction of 0-deutero-/3-( p-anisyl )-j3-phenyIpropionaldehyde with di-i-butyl peroxide has been found to give decarbonylation without rearrangement of the deuterium atom. A reinvestigation of the decarbonylation of ,3,/3,0-triphenyIpropionaldehyde has shown that in addition to the 1,1,2-triphenylethane previously reported there are present lesser amounts of triphenylethylene and 3,3-diphenyl-l-indanone. Decarbonylation of ß-(p-nitrophenyl)-,3,5-diphenylpropionaldehy de proceeded to only a small extent and led to the rearranged olefin, 2-( p-nitrophenyl )-l, 1-diphenylethylene, as the only product which could be characterized.

Free-Radical Rearrangements

“…Rearrangements that do not have such thermodynamic driving forces and are not assisted by the gera-dialkyl effect are much slower, e.g., rearrangement of isotopically labeled 2-phenylethyl radicals (64,70) (Table 1) and of the (C 6 H 5 ) 2 CH 14 CHC 6 H 5 radical (77). This was initially observed for groups attached to the migrating aromatic nucleus (73)(74)(75) and was attributed to the transition state having some polar character and being stabilized by charge separation as indicated below, the extent of the polar contribution (i.e., 7b and 7c) increasing as X became more electron withdrawing: .…”

“…Finally, the ease of ring opening of the intermediate spirohexadienyl radical should reflect the stability of the product. Other examples of Ar 2 -5 cycliza tion include the formation of indanones (74,88), e.g., 157 -> 158 -> 159 (88), and ring closure of PhOCOCH 2 ' (351), 2-arylbenzoyl radicals (352), PhCH=CHÒH 2 (353), and PhC(CH 2 CH 2 )CH 2 CH 2 (119). Numerous examples of ring closure in arylalkyl and similar radicals have been summarized in previous reviews (4, 6-6b).…”

Chemistry of Acyl Radicals

“…249 Curtin and Kauer studied the pyrolysis of , , -triphenylpropionaldehyde (92) in the presence of ditert-butyl peroxide and observed a meager yield of a diphenylindanone 93, together with 1,1,2-triphenylethane (94) resulting from decarbonylation and a subsequent neophyl rearrangement (Scheme 102). 250 Urry and co-workers described an interesting reaction in which a 4-phenylbutyraldehyde (95) was heated to 100°C in the presence of a peroxide initiator. The products were the expected decarbonylated species (96), that of a formal 6-endo-ring closure (97) and, most interestingly, a rearranged species (98) resulting from ipso-substitution on the aromatic ring (Scheme 103).…”

“…Curtin and Kauer studied the pyrolysis of β,β,β-triphenylpropionaldehyde ( 92 ) in the presence of di- tert -butyl peroxide and observed a meager yield of a diphenylindanone 93 , together with 1,1,2-triphenylethane ( 94 ) resulting from decarbonylation and a subsequent neophyl rearrangement (Scheme ) 102 …”

Substituent effects at the origin of a free-radical 1,2-aryl migration and in the related disproportionation reaction of 10-hydro-9-p-X-phenyl-9-phenanthryl radicals

“…The (9-p-X-phenyl-9-fluorenyl)acetaldehydes (5, X = H, CH3, Cl, F, OCH3, or SCH3)15 were synthesized from fluorenone and the appropriately substituted phenylmagnesium bromide by a procedure analogous to that described by Nesmeyanov et al 16 and by Curtin and Hurwitz4 in an average overall yield of 45%.…”