Straightforward Synthesis of a Vicinal Double‐Bridgehead Iodo Trimethylsilyl Octacycle: Unprecedented Lack of Reactivity of the Silyl Group in the Presence of Fluoride Anions

Abstract

A convenient synthesis of an octacyclic compound containing an iodo and a trimethylsilyl group in vicinal double‐bridgehead positions, as a possible precursor of a pyramidalized alkene, is described. The key step of the synthesis consists of a double nucleophilic substitution of two neopentyl‐type iodides by cyclopentadienide anions followed by two intramolecular Diels–Alder cycloadditions. All attempts to generate the expected pyramidalized alkene from the above precursor on reaction with different sources of fluoride failed. This octacyclic compound, which contains two disubstituted C=C bonds, underwent a chemo‐ and stereoselective Pd0‐catalyzed co‐cyclotrimerization with dimethyl acetylenedicarboxylate to give a nonacyclic cyclohexadiene derivative that can be aromatized upon reaction with CsF or transformed into a related fluoride upon reaction with AgF.

Generation and Reactions of an Octacyclic Hindered Pyramidalized Alkene

“…Recently, we have described 21 To solve this problem, we have prepared diiodide 38 according to Scheme 3. 5,5-…”

“…Recently, we have described 21 the preparation of octacycle 28 as a possible precursor of pyramidalized alkene 27 (Scheme 2) by reaction with fluoride anions, following the procedure described by Lukin and Eaton 19 to generate cubene 15. However, all attempts to generate 27 on reaction with CsF alone or in combination with AgF in the presence of dienes, such as 1,3diphenylisobenzofuran, tetraphenylcyclopentadienone, furan, or anthracene at different temperatures, left the starting compound unchanged.…”

“…1 H NMR (400 MHz, CDCl 3 ): δ = 0.96 [s, 9H, C(CH 3 ) 3 ], 1.37 (overlapped dd, 2 J (H,H) = 14,8 Hz, 3 J (H,H) = 2.8 Hz, 1H) and 1.39 (overlapped dd, 2 J (H,H) = 14.8 Hz, 3 J (H,H) = 2.8 Hz, 1H) (18-H a and 18-H b ), 1.41 (overlapped dd, 2 J (H,H) = 14.0 Hz, 3 J (H,H) = 2.8 Hz, 1H), and 1.43 (overlapped dd, 2 J (H,H) = 14.0 Hz, 3 J (H,H) = 2.8 Hz, 1H) (2-H a and 2-H b ), 1.50 (s, 1H, 10-H), 1.57 (d, 3 J (H,H) = 6.0 Hz, 1H, 11-H), 1.63 (d, 4 J (H,H) = 1.6 Hz, 1H, 19-H), 1.68 (s, 1H, 9-H), 1.77−1.81 (complex signal, 2H, 3-H and 17-H), 2.22−2.24 (broad s, 1H, 4-H), 2.27 (d, 3 J (H,H) = 6.0 Hz, 1H, 12-H), 2.30 (broad s, 1H, 13-H), 2.38 (broad s, 1H, 16-H), 2.41−2.43 (broad s, 1H, 7-H), 5.95 (dd, 3 J (H,H) = 5.6 Hz, 4 J (H,H) = 3.2 Hz, 1H, 5-H), 6.03 (overlapped dd, 3 J (H,H) = 5.6 Hz, 4 J (H,H) = 3.2 Hz, 1H, 15-H), 6.05 (overlapped dd, 3 J (H,H) = 5.6 Hz, 4 J (H,H) = 3.2 Hz, 1H, 14-H), 6.24 ppm (dd, 3 J (H,H) = 5.6 Hz, 4 J (H,H) = 3.2 Hz, 1H, 6-H). 13 Reaction of Diiodide 38 with Na/Hg in the Presence of 11,12-Dimethylene-9,10-dihydro-9,10-ethanoanthracene 14: Isolation of (3s,4R,7S,8R,9S,10s,11R,12S,13R,16S,17s,19s)-Octacyclo[10.6.1.0 1,10 .0 3,7 .0 4,9 .0 8,19 .0 11,16 .0 13,17 6,24 .0 1,28 .0 2,30 .0 3,18 .0 3,27 .0 4,16 .0 4,25 .0 5,13 .0 6,15 .0 8,12 .0 9,14 .0 16,23 .0 17,21 .0 20,27 .0 22,…”