Using a Temporary Silicon Connection in a Highly Stereoselective Synthesis of a New Class of Cyclic Allenylsilanes

Abstract

Aldehyde 4 reacts in the presence of TMSOTf and an acid scavenger to provide the corresponding oxasilacycle 5 in very good yield and as a single diastereoisomer. The sense of 1,3-ste­reoinduction serves to introduce a 1,3-syn-diol relationship into the cyclic product. This is in accord with a previous study involving an analogous intramolecular allylation.

Key words

cyclisations - intramolecular allenylation - Lewis acids - stereoselective synthesis - Temporary Silicon Connection

References

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1

Current address: Metcalf Center for Science and Engineering, Boston University, 590, Commonwealth Avenue, Boston, MA 02215-2521, USA.

4

Tri-tert-butylpyrimidine (TTBP) and 2,6-di-tert-butyl-4-methylpyridine (2,6-DTBMP) were equally effective in this role.

11

The silyl tether is part of a vinylsilane in this intermediate and will be less effective in stabilising the β-vinyl carbocation on geometric grounds.

15

Propargyltrimethylsilane is commercially available although expensive and invariably contaminated with varying amounts of allenyltrimethylsilane. We find it more convenient to prepare the reagent ourselves.