Transoid Homoallylic Proton-Proton Coupling Constants

Abstract

Transoid homoallylic coupling constants (5JH,H) for six compounds (5,10-dihydroindeno[2,1-alindene and confertifolin derivatives) of fixed stereochemistry were determined and compared with calculated values. Magnetic equivalence limited discrete determination of 5Jtrans and 5Jcis to three of these compounds. The single compound where unequivocal assignment could be made revealed 5Jtrans > 5Jcis; this was supported in two other compounds by tentative assignment. Changes in the magnitude of the couplings suggested that substantial substituent effects may be operative. INDO-MO calculations correctly predicted the angular dependence but incorrectly predicted 5Jcis > 5Jtrans.

Structures of Saturated 5H‐Pyrrolo[1,2‐a][3,1]benzoxazin‐1(2H)‐ones Prepared from 4‐Oxopentanoic Acid and Cyclic Amino Alcohols

“…As for 4, the carbocycle of 5a is also in a half-chair conformation because of the C-7ϪC-8 double bond. In contrast to the trans-fused compounds, the sin 2 ϕ sin 2 ϕЈ-dependent [27,28] homoallylic 5 J 9a-H,2-Hsyn couplings had zero values in 3 and 5a, indicating that the torsion angle between 9a-H and C-1 is now much closer to 0°. Such an arrangement also places 9a-H in the deshielding zone of the lactamide carbonyl bond, which is clearly reflected by the considerable downfield shift (Ͼ 1 ppm) experienced by this proton in comparison to the trans-fused derivatives.…”

Synthesis of albidin (6-methoxy-3-methylisobenzofuran-4,5-dione) and (±)-curvulol [(±)-1,3-dihydro-6-methoxy-3-methylisobenzofuran-4,5-diol]

“…92-95 "C (Found: C, 61. (12), 123 (26), 121 (14), 109 (17), 108 (lo), 107 (lo), 93 (lo), 80 (12), 79 (12), 67 (12), 65 (16), 53 (20), 51 (12), and 43 (68); v,,,,(KBr) 1 663 and 1 630 cm-'.…”

“…(1 H, ddq, J1.4 < 1.0 Hz, J1,3cis 1.6 Hz, J1,3trans 2.8 Hz, J 6.3 2-Bromo-3,4,5-trimethoxybenzyl Vinyl Ether (16).-A solution of the bromobenzyl alcohol (9) (2.00 g, 7.22 mmol), Hg(OAc), (90 mg, 0.3 mmol) in ethyl vinyl ether (1 1.4 g, 0.16 mol) was refluxed for 2 days under N,. On cooling the reaction mixture was diluted with Et,O, washed with saturated NaHCO,, then H,O, dried and evaporated.…”

“…On cooling the reaction mixture was diluted with Et,O, washed with saturated NaHCO,, then H,O, dried and evaporated. Flash chromatography (EtOAc-light petroleum) of the crude product gave the vinyl ether (16) as a colourless oil (1.17 (10). Further elution gave unchanged benzyl alcohol (9) (0.77 g, 39%).…”

“…Further elution gave unchanged benzyl alcohol (9) (0.77 g, 39%). (16).-A solution of the vinyl ether (16) (226 mg, 0.75 mmol), Bu,SnH (435 mg, 1.50 mmol) and 2,2'-azobisisobutyronitrile (AIBN) (10 mg) in dry C6H6 (75 ml) was refluxed under N, for 4 h. The reaction mixture was evaporated in uucuo and flash chromatography of the crude product gave an oil which was distilled (125-150 "C/O.l mm) to give a colourless oil (171 mg). G.c.m.s.…”