An Expedient Entry to Chromane Derivatives via Indium-Mediated ­Intramolecular Allenylation Reactions

Abstract

Starting from salicylaldehydes and 1,4-dibromo-2-butyne, preparation of chromane derivatives has been investigated. After attaching the bromobutynyl tether followed by intramolecular allenylation of aldehydes (or ketones) promoted by indium in aqueous (or organic) media, the chromane derivatives with allenic ­moiety have been efficiently constructed. The direct one-pot preparation of the chromanes has also been achieved.

Key words

chromane - indium - intramolecular allenylation reactions - synthesis - cyclizations

References

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6

Typical Procedure: Preparation of 3-Vinylidene-chroman-4-ol (Table [5] , entry 1). To a solution of K₂CO₃ (133 mg, 0.96 mmol) and KI (13 mg, 0.08 mmol) in DMF (2 mL) were added salicylaldehyde (98 mg, 0.80 mmol) and 1,4-dibromo-2-butyne (169 mg, 0.80 mmol). The solution was stirred at r.t. for 10 h until the reaction was completed (monitored by TLC). The solution was neutralized by adding HOAc (ca 1.2 equiv). After addition of In (184 mg, 1.60 mmol) additional HOAc was added until the pH of the solution became 5. The resulting solution was stirred for 1 h. After the reaction was completed, the solution was extracted with Et₂O (2 × 20 mL). The organic layer was dried (MgSO₄) and concentrated. Flash chromatography (hexanes-EtOAc, 7:1) provided the desired product (97 mg, 70%) as a white solid; mp 54-56 °C. ¹H NMR (300 MHz, CDCl₃): δ = 7.4-6.9 (m, 4 H, ArH), 5.22 (s, 1 H, CHOH), 5.02 (s, 2 H, C=C=CH ₂), 4.77 (d, 1 H, J = 11.6 Hz, -OCHHC), 4.64 (d, 1 H, J = 11.6 Hz, -OCHHC). ¹³C NMR (75.5 MHz, CDCl₃):
δ = 204.2, 154.1, 129.8, 128.9, 123.9, 121.1, 117.1, 97.4, 78.5, 65.5, 64.6. MS(EI): m/z (%) = 174 [M⁺], 157, 156, 155, 145, 131, 128, 122, 121(100), 104, 77, 51. HRMS: m/z calcd for C₁₁H₁₀O₂: 174.0681; found: 174.0682.