Studies towards the Synthesis of Lindenene: Unexpected Stereochemical Outcome of an Intramolecular Cyclopropanation Reaction and Synthesis of (±)-epi-Lindenene and (±)-iso-Lindenene

Abstract

Investigation towards the synthesis of the furanosesqui­terpene Lindenene using an intramolecular cyclopropanation reaction gave unexpected ring-junction isomerisation products. These products were elaborated to (±)-epi-lindenene and (±)-iso-lindenene.

Key words

furanosesquiterpene - Hagemann’s ester - cyclopropanation - isomerisation - Julia-Kocienski methylenation

References and Notes

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12

Spectral data for epi-lindenene (12): IR (thin film): 3075, 3005, 2923, 1658, 1451, 1088, 868 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.65-0.71 (1 H, m), 0.89-0.93 (1 H, m), 1.13 (3 H, s, CH₃), 1.47-1.51 (1 H, m), 1.84-1.90 (1 H, m), 1.94 (3 H, s, CH₃), 2.00-2.03 (1 H, m), 2.41-2.43 (1 H, m), 2.44-2.47 (2 H, m), 2.61 (1 H, d, J = 11.5 Hz), 4.48 (1 H, s, R₂C=CH₂), 4.91 (1 H, s, R₂C=CH₂), 7.03 (1 H, s). ¹³C NMR (100 MHz, CDCl₃): δ = 8.19, 10.35, 15.93, 21.73, 23.33, 30.67, 34.12, 39.60, 41.09, 101.52, 114.16, 119.47, 136.96, 148.48, 152.56. HRMS (ESI): m/z [M + Na]⁺ calcd for C₁₅H₁₈NaO: 237.1250; found: 237.1250.

13

Spectral data for iso-lindenene (13): ¹H NMR (400 MHz, CDCl₃): δ = 0.64-0.70 (1 H, m), 0.88 (3 H, s, CH₃), 0.89-0.95 (1 H, m), 1.44-1.49 (1 H, m), 1.85-1.89 (1 H, m), 1.93 (3 H, s, CH₃), 1.96-2.00 (2 H, m), 2.47-2.52 (2 H, m), 2.66 (1 H, d, J = 15.5 Hz), 4.66 (1 H, s, R₂C=CH₂), 4.98 (1 H, s), 7.09 (1 H, s). ¹³C NMR (100 MHz, CDCl₃): δ = 8.10, 9.92, 17.96, 20.24, 23.10, 28.27, 34.62, 40.74, 42.04, 102.34, 117.37, 119.75, 137.55, 151.34, 152.21. HRMS (ESI): m/z [M + Na]⁺ calcd for C₁₅H₁₈NaO: 237.1250; found: 237.1250.