A Highly Diastereoselective Access to Silicon-Containing Oxazines via the TMSOTf-Promoted Reactions of N-Benzoyl-N,O-acetals with Allyl Silanes

Abstract

A TMSOTf-promoted cycloaddition of N-benzoyl-N,O-acetals with allyl silanes to synthesize silicon-containing oxazines with high diastereoselectivities has been developed. The obtained products might be useful as building blocks in organic synthesis.

N-benzoyl-N,O-acetals - oxazine - cycloaddition - dia­stereoselectivity

Reference and Notes

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12

Typical Procedure for the Preparation of Oxazines (13b)
To a mixture of 11a (1 mmol), tert-butyl trimethyl allyl silane (1 mmol) and CH₂Cl₂ (10 mL) was added TMSOTf (0.16 mL, 1 mmol) dropwise at -78 ˚C. After stirring at the same temperature for 1 h, the reaction was quenched by the addition of sat. NaHCO₃ solution (10 mL). The resulting mixture was extracted with CH₂Cl₂ (3 × 10 mL). The combined organic extracts were washed with brine, dried over Na₂SO₄. Removal of the solvent provided the residue which was purified by flash chromatography to afford trans-13b (244 mg, 67%) and cis-13b (40.7 mg, 11%) as colorless oils.
trans-13b: ^¹H NMR (400 MHZ, CDCl₃): δ = 7.94 (d, J = 8.0 Hz, 2 H), 7.34-7.13 (m, 8 H), 4.63 (dd, J = 11.6, 4.8 Hz, 1 H), 4.47-4.40 (m, 1 H), 2.23-2.18 (m, 1 H), 1.47 (dd, J = 24.4, 11.6 Hz, 1 H), 1.05 (dd, J = 14.8, 8.0 Hz, 1 H), 0.87 (dd, J = 14.8, 6.0 Hz, 1 H), 0.81 (s, 9 H), 0.05 (s, 3 H), 0.00 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 156.4, 144.7, 134.2, 130.4, 128.4, 128.0, 127.4, 126.7, 126.4, 74.2, 57.1, 40.6, 26.4, 20.3, 16.5, -4.8, -5.3. ESI-MS: m/z = 366 [M + 1]. Anal. Calcd for C₂₃H₃₁NOSi: C, 75.56; H, 8.55; N, 3.83. Found: C, 75.47; H, 8.37, N, 3.95.
cis-13b: ^¹H NMR (400 MHz, CDCl₃): δ = 8.02 (d, J = 8.0 Hz, 2 H), 7.41-7.20 (m, 8 H), 4.88 (t, J = 4.8 Hz, 1 H), 4.29-4.23 (m, 1 H), 2.06-1.95 (m, 2 H), 1.17 (dd, J = 14.4, 8.0 Hz, 1 H), 0.89 (dd, J = 14.8, 6.8 Hz, 1 H), 0.82 (s, 9 H), 0.00 (s, 3 H), -0.05 (s, 3 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 156.5, 144.5, 134.2, 130.4, 128.3, 128.0, 127.3, 126.8, 126.6, 70.2, 54.3, 37.6, 26.3, 19.8, 16.5, -5.1, -5.3. HRMS: m/z calcd for C₂₃H₃₂NOSi [M + H]⁺: 366.2253; found: 366.2263.