New Chiral Propargylic Silanes and the First Examples of Asymmetric Intramolecular Sakurai Reactions

Abstract

The syntheses of four new chiral propargylic silanes are reported. The syntheses of these cyclization precursors offer the possibility of studying the asymmetry of the first examples of the intramolecular version of the Sakurai reaction.

Key words

chiral auxiliaries - cyclizations - Lewis acids - Sakurai reaction - spiro compounds

References

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10

The enantiomeric excesses of compounds 2 and 13 were determined by chiral GC column chromatography and verified by racemic samples of 2 and 13.

17

X-ray analysis of compound 17: C₁₉H₃₀OSi, M = 302.52, orthorhombic, space group P2 ₁ 2 ₁ 2 ₁ , a = 10.1154(6) Å, b = 13.3330(10) Å, c = 14.0385(3) Å, U = 1839.35(19) ų, Z = 4, D = 1.061 Mgm^-3, F(000) = 664, µ (MoK_α) = 0.122 mm^-1, max/min transmission 1.00/0.58, colorless plate 0.52 × 0.16 × 0.05 mm, T = 173(2) K. Siemens SMART CCD system with MoK_α X-radiation (λ = 0.71073 Å) and graphite monochromator, 12366 reflections over a range of 2.11° < θ < 28.16°, absorption correction with the SADABS routine. Structure refinement: Anisotropic on F ^² (program SHELXL-93. G. M. Sheldrick, University of Göttingen). H atoms riding or as rigid methyl groups; R1 = 0.0607 (conventional) and wR2 = 0.1317 (all data), with goodness of fit = 0.991 for 195 refined parameters. Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre under the number 6974. Copies may be obtained without charge from: CCDC, Union Road, Cambridge CB2 1EZ, UK (Fax: [phone]; E-mail: [e-mail]).