Effect of Chain Length on Radical to Carbanion Cyclo-Coupling of Bromoaryl Alkyl-Linked Oxazolines:  1,3-Areneotropic Migration of Oxazolines

Abstract

2-Halophenylalkyl-2-oxazolines with alkyl chain spacers of two to six C atoms (n = 0-4) were prepared and their SRN1-type reactions with several base systems examined. The best conditions to promote cyclo-coupling to the corresponding benzocycloalkane derivatives involved use of LDA in THF. The precursors with 3-C-atom and 4-C-atom spacers gave good yields of 2-(1'-phenylindan-1'-yl)-2-oxazolines and 2-(1-phenyl-1,2,3,4-tetrahydronaphthalen-1-yl)-2-oxazoline, respectively. The major products from the precursor with a 5-C-atom spacer were derivatives of benzocycloheptane in which the oxazoline group had undergone a novel areneotropic migration from the end of the spacer to the benzo ring. The product from reaction of the corresponding 2-C-atom precursor was a 9-oxazolinophenanthrene derivative. EPR spectroscopy showed the intermediates of the LDA-promoted reactions to be radical anions of the product benzocycloalkanes. This supported an SRN1-type chain mechanism involving initial production of aryl radicals connected to azaenolate ions via the spacer groups. Intramolecular radical to carbanion coupling then generated ring-closed benzocycloalkane radical anions that transferred an electron to more precursor. Diastereoselective radical to carbanion cyclo-coupling reactions were carried out with 2-bromophenylpropyl precursors containing chiral 2-oxazolines. The diastereoselectivity achievable was modest, but the product diastereoisomeric Indane derivatives were easily separable by chromatography.

Electron-Transfer-Mediated Synthesis of Phenanthridines by Intramolecular Arylation of Anions from N-(ortho-Halobenzyl)arylamines: Regiochemical and Mechanistic Analysis

“…24-7.30 (1H, m), 7.36 (1H, d, J = 7.5 Hz), 7.85 (1H, d, J = 7. 8 Hz); 13 C NMR (CCl 3 D) δ 52.9, 55.5, 98.4, 109.5, 110.2, 116.8, 121.2, 128.3, 128.5, 128.8, 137.6, 139.3, 141.0, 146.8; GC-MS (m/z) 340 (M þ þ 1, 15), 339 (M þ , 100), 324 (23), 217 (48), 210 (12), 196 (12), 180 (22), 136 (17), 120 (16), 94 (12), 92 (11), 91 (11), 90 (27), 89 (13), 77 (11), 65 (16); HRMS (ESI/APCI) calcd for C 14 H 15 INO 340.0193, found 340.0198.…”

Theoretical Study on Reaction of Furan Anion with N2O in Gas Phase

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, they have not been successfully isolated, possibly due to their high reactivities. [10][11][12]15 Previously, the substantial efforts were made to prepare and characterize carbanions experimentally, [13][14][15] for example, in 1977, Depuy et al 17 investigated experimentally the different reactions of carbanions with N 2 O, CS 2 and CO 2 , respectively. The detailed mechanistic studies were performed emphatically on N 2 O with the dissimilar carbanions in 1986.…”

Theoretical investigation on carbon-centered tri-s-tetrazine and its 10 derivatives

“…It is a reactive intermediate [22][23][24] and is often encountered in organic chemistry (for instance, in the E1cB elimination reaction [25]), in organometallic chemistry (for instance, in Grignard reaction [26][27][28][29][30][31][32][33][34]) or in alkyl lithium chemistry. Many experiments demonstrate that stable carbanions do exist [22][23][24][25][26][27][28][29][30][31][32][33][34][35]. However, they have not been isolated, possibly due to their high reactivities [28][29][30]35].…”

“…Many experiments demonstrate that stable carbanions do exist [22][23][24][25][26][27][28][29][30][31][32][33][34][35]. However, they have not been isolated, possibly due to their high reactivities [28][29][30]35]. Substantial efforts have been made to prepare and characterize stable carbanions experimentally [31][32][33][34].…”