<A NAME="RD18205ST-4B">4b</A>
Typical Experimental Procedure for the Synthesis of Tetracycle 3.
A flame dried microwave tube was charged with (1R,3R,7R,8S)-4-bromo-3-ethynyl-1-methoxy-8-methyl-2-oxatricyclo[5.3.1.03,8]undec -4-ene (4, 200 mg, 0,67 mmol), cyclopent-2-enone (0.11 mL, 110 mg, 1.34 mmol) and Et3N (0.28 mL, 203 mg, 2.01 mmol) under nitrogen. The tube was sealed and irradiated
under microwave conditions until a temperature of 110 °C was reached. The temperature
was maintained for a further 5 min and the reaction mixture was rapidly cooled. The
reaction mixture was partitioned between brine 10 mL and Et2O (3 × 20 mL). The combined organic layer was dried (MgSO4), filtered and concentrated. Purification of the resulting crude dark oil using flash
silica chromatography with 20% Et2O-PE (60:80) gave the title compound 3 (48%) and the ketone 17 (10%).
Physical Data for 3.
R
f
= 0.56 (Et2O-PE 1:1). IR: νmax = 2974 (C=C-H), 2933 (sat. C-H), 1714 (α,β-unsat.C=O) cm-1. [α]D
24 -81.4 (c 1.02, CHCl3).
ESI-MS [M + Na]+
(amu): 323.1616 (found), 323.1618 (calcd; 0.2 mmu difference).
LRMS (EI): m/z (%) = 300(100) [M+
], 285 (9) [M+
- Me], 272 (12) [M+
- CO].
H1 NMR (300 MHz, CDCl3): δ = 0.69 (s, 3 H, C-CH3), 1.40 (m, 1 H, 7-Hα), 1.52 (ddd, 1 H J = 13.6, 12.5, 5.0 Hz, 16-Hα), 1.65-2.00 (m, 6 H, 12-H, 13-H, 11-Hα, 13-H, 15-H), 2.14 (d, 3 H, J = 2.9 Hz, =C-CH3), 2.17-2.31 (m, 3 H, 11-Hβ, 7-Hβ, 16-Hβ), 2.40-2.55 (m, 2 H, 6-H), 3.23 (s, OCH3), 3.85 (m, 1 H, 8-H), 5.39 (m, 1 H, 10-H) ppm.
13C NMR (75 MHz, CDCl3): δ = 13.0 (q), 19.4 (q), 27.3 (t), 30.1 (s), 30.7, 30.9, 31.2 (t), 37.0 (d), 37.1
(t), 44.0 (t), 48.5 (d), 50.0 (q), 93.5 (s), 98.1 (s), 117.0 (d), 143.9, 145.1, 145.9
(s), 204.4 (s) ppm.
