A Short and Efficient Total Synthesis of (+)-Deoxoprosopinine via Diastereoselective Allylation of the Bicyclic N-Acyl Iminium Ion Formed in situ with a π-Nucleophile

Abstract

A short and efficient synthesis of (+)-deoxoprosopinine is reported involving Miyashita endoselective epoxide ring-opening reaction, diastereoselective allylation of the bicyclic N-acyl iminium ion formed in situ with a π-nucleophile, and olefin cross-metathesis as the key steps.

Key words

Miyashita epoxide opening - diastereoselectivity - allylation - cross-metathesis, piperidines

• References and Notes

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• 9 Compound 7: Yellow oily liquid; [α]_D ²⁵ –13.1 (c 1.11, CHCl₃). ¹H NMR (500 MHz, CDCl₃): δ = 7.68–7.58 (m, 4 H, Ar-H), 7.45–7.33 (m, 6 H, Ar-H), 3.85 (dd, J = 5.2, 1.3 Hz, 2 H, OCH₂), 3.76–3.72 (m, 1 H, OCH), 3.70 (t, J = 4.9 Hz, 2 H, OCH₂), 3.33 (q, J = 5.1 Hz, 1 H, -N₃CH), 1.92–1.78 (m, 1 H), 1.72 (quint, J = 6.4 Hz, 2 H), 1.65–1.53 (m, 1 H), 1.05 (s, 9 H, t-Bu). ¹³C NMR (75 MHz, CDCl₃): δ = 135.5, 132.9, 129.8, 127.7, 72.7, 66.5, 64.3, 63.1, 31.6, 28.6, 26.7, 19.0. HRMS: m/z [M + Na]⁺ calcd for C₂₂H₃₁N₃O₃NaSi: 436.2032; found: 436.2052.Compound 9: White solid; mp 71–72 °C; [α]_D ²⁵ –43.9 (c 0.90, CHCl₃). ¹H NMR (300 MHz, CDCl₃): δ = 7.66–7.60 (m, 4 H, Ar-H), 7.40–7.32 (m, 6 H, Ar-H), 7.31–7.26 (m, 5 H, Ar-H), 5.09–5.00 (m, 2 H, OCH₂), 4.49 (d, J = 8.7 Hz, 1 H, NH), 3.87 (td, J = 6.7, 3.8 Hz, 1 H, OCH), 3.66 (t, J = 4.8 Hz, 2 H, OCH₂), 3.57–3.49 (m, 1 H, NCH), 3.48–3.40 (m, 2 H, OCH₂), 1.84–1.64 (m, 2 H), 1.61–1.37 (m, 2 H), 1.32 (s, 6 H), 1.05 (s, 9 H, t-Bu). ¹³C NMR (75 MHz, CDCl₃): δ = 155.6, 136.1, 135.5, 133.9, 133.8, 129.5, 128.5, 128.1, 128.0, 127.5, 98.7, 72.0, 66.9, 63.4, 63.2, 50.1, 28.8, 28.0, 27.9, 26.9, 19.9, 19.2. HRMS: m/z [M + Na]⁺ calcd for C₃₃H₄₃NO₅NaSi: 584.2808; found: 584.2805.Compound 11: Syrupy liquid; [α]_D ²⁵ –33.1 (c 1.20, CHCl₃). ¹H NMR (600 MHz, CDCl₃): δ = 7.40–7.30 (m, 5 H, Ar-H), 5.70–5.63 (m, 1 H, olefinic), 5.11–4.99 (m, 4 H, 2 × olefinic, -OCH₂Ph), 4.52–4.40 (m, 3 H, OCH₂, NCH), 3.68 (dt, J = 10.2, 3.9 Hz, 1 H, OCH), 3.21 (dt, J = 10.2, 6.1 Hz, 1 H, NCH), 2.53–2.46 (m, 1 H, allylic), 2.34–2.26 (m, 1 H, allylic), 1.80–1.53 (m, 4 H), 1.49 (s, 3 H), 1.39 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 155.2, 136.5, 134.6, 128.4, 128.0, 127.9, 117.4, 98.2, 70.9, 67.0, 62.7, 53.4, 52.3, 34.1, 25.9, 25.6, 19.0. HRMS: m/z [M + Na]⁺ calcd for C₂₀H₂₇NO₄Na: 368.1837; found: 368.1834.Compound 5: Oily liquid; [α]_D ²⁵ –35.4 (c 0.17, CHCl₃). ¹H NMR (300 MHz, CDCl₃): δ = 7.42–7.32 (m, 5 H, Ar-H), 5.58–5.42 (m, 1 H, olefinic), 5.32–5.21 (m, 1 H, olefinic), 5.10–5.04 (m, 2 H, OCH₂Ph), 4.53–4.34 (m, 3 H, OCH_2, OCH), 3.69 (dt, J = 8.3, 3.7 Hz, 1 H, NCH), 3.28–3.17 (m, 1 H, NCH), 2.52–2.16 (m, 4 H, allylic), 2.11–1.81 (m, 4 H), 1.52 (s, 3 H), 1.42 (s, 3 H), 1.37–1.18 (m, 14 H), 0.9 (t, J = 8.3 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 151.5, 133.8, 133.5, 128.4, 128.0, 127.8, 127.1, 125.6, 71.0, 67.0, 63.0, 62.6, 54.0, 53.5, 52.8, 33.0, 32.6, 32.0, 29.7, 29.5, 29.2, 29.0, 27.1, 26.6, 26.0, 25.5, 22.7, 19.1, 14.1. HRMS: m/z [M + Na]⁺ calcd for C₂₉H₄₅NO₄Na: 494.3246; found: 494.3224.Compound 1: Colorless solid; mp 89 °C; [α]_D ²⁵ +15.5 (c 0.43, CHCl₃) {Lit.^4b,c [α]_D ²⁰ +14.6 (c 0.3, CHCl₃), Lit.^4d [α]_D ²³ +12.2 (c 0.015, CHCl₃), Lit.^4e [α]_D ²⁵ +15.3 (c 0.3, CHCl₃)}. ¹H NMR (300 MHz, CDCl₃): δ = 3.69–3.60 (m, 2 H, OCH₂), 3.58–3.49 (m, 1 H, OCH), 2.88 (q, J = 5.4 Hz, 1 H, NCH), 2.82–2.72 (m, 1 H, NCH), 2.33 (br s, 3 H), 1.79–1.44 (m, 4 H), 1.27 (s, 22 H), 0.88 (t, J = 6.7 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 67.9, 62.2, 58.0, 49.9, 33.7, 31.9, 29.6 (6C), 29.3, 28.5, 27.2, 26.3, 22.6, 14.1. HRMS: m/z [M + H]⁺ calcd for C₁₈H₃₈NO₂: 300.2902; found: 300.2911.