Double Nucleophilic Addition of Azide and Tetraallyltin to the Latent α,β-Unsaturated Aldehydes Using in situ Hydrolysis of the Imino Functionality Promoted by Tin(IV) Chloride Pentahydrate

Abstract

In the presence of SnCl₄·5H₂O and acetic acid, a mixture of trimethylsilyl azide and tetraallyltin underwent 1,4- and sub­sequently 1,2-addition, respectively, with the α,β-unsaturated ­aldimines to give 1,3-hydroxy azides in good yields, where the hydrolysis of the intermediary imino species was found to be crucial.

Key words

α,β-unsaturated aldimine - conjugate addition - imino compound - Lewis acid

References

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8

A Typical Procedure for the Addition Reaction (Table 1, Entry 6): To a suspension of SnCl₄·5H₂O (24.5 mg, 0.07 mmol) in CH₂Cl₂ (1.2 mL) was added trimethylsilyl azide (0.1 mL, 0.75 mmol) and HOAc (0.04 mL, 0.70 mmol) successively at -78 °C, and the mixture was stirred at -78 °C for 15 min. A solution of N-diphenylmethylhexenyl-idenamine (3a) (36.9 mg, 0.14 mmol) in CH₂Cl₂ (1.5 mL) was added to the resulting mixture at -78 °C, and the mixture was stirred at -78 °C for 10 min. A solution of tetraallyltin (19.8 mg, 0.07 mmol) in CH₂Cl₂ (1.5 mL) was added to the resulting mixture at -78 °C and the mixture was gradually warmed to r.t. during 17.3 h. Sat. aq NaHCO₃ was added to the mixture which was extracted with EtOAc. The combined extracts were dried (Na₂SO₄) and concentrated in vacuo to give a crude oil. Purification on silica gel TLC (n-hexane:EtOAc = 10: 1 as an eluent) gave 6-azidonon-1-en-4-ol (4a) (21.1 mg, 82%) with a diastereomer ratio of 64:36 as a colorless oil. ¹H NMR (500 MHz, CDCl₃): δ = 0.95 (t, 3 H, J = 7.2 Hz), 1.39-1.70 (m, 6 H), 1.91 (brs, 1 H), 2.15-2.34 (m, 2 H), 3.47-3.52 (m, 0.36 H), 3.61-3.66 (m, 0.64 H), 3.78-3.83 (m, 0.36 H), 3.86-3.91 (m, 0.64 H), 5.14-5.18 (m, 2 H), 5.78-5.86 (m, 1 H). IR (neat): 3400, 2950, 2900, 2850, 2800, 2100, 1650, 1570, 1530, 1470 cm^-1.

9

For the allylation of the intermediary imino species 5, we could obtain 3-amino azides by using SnCl₄ in place of SnCl₄·5H₂O under anhydrous conditions. These results will be reported in due course.