Exceptionally E‐ and β‐Selective NHC–Cu‐Catalyzed Proto‐Silyl Additions to Terminal Alkynes and Site‐ and Enantioselective Proto‐Boryl Additions to the Resulting Vinylsilanes: Synthesis of Enantiomerically Enriched Vicinal and Geminal Borosilanes. Issue 9 (16th January 2013)

• Record Type: Journal Article
• Authors: Meng, Fanke; Jang, Hwanjong; Hoveyda, Amir H.
• Is Part Of: Chemistry. Volume 19:Issue 9(2013)
• Page Start: 3204
• Page End: 3214
• Publication Date: 2013-01-16
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201203803
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>An exceptionally site‐ and <italic>E‐</italic>selective catalytic method for preparation of Si‐containing alkenes through protosilylation of terminal alkynes is presented. Furthermore, the vinylsilanes obtained are used as substrates to generate vicinal or geminal borosilanes by another catalytic process; such products are derived from enantioselective protoborations of the Si‐substituted alkenes. All transformations are catalyzed by N‐heterocyclic carbene (NHC) copper complexes. Specifically, a commercially available imidazolinium salt, cheap CuCl (1.0 mol %) and Me<sub>2</sub>PhSi–B(pin), readily and inexpensively prepared in one vessel, are used to convert terminal alkynes to (<italic>E</italic>)‐β‐vinylsilanes efficiently (79–98 % yield) and in >98 % <italic>E</italic> and >98 % β‐selectivity. Vinylsilanes are converted to borosilanes with 5.0 mol % of a chiral NHC–Cu complex in 33–94 % yield and up to 98.5:1.5 enantiomeric ratio (e.r.). Alkyl‐substituted substrates afford vicinal borosilanes exclusively; aryl‐ and heteroaryl‐substituted alkenes deliver the geminal isomers preferentially. Different classes of chiral NHCs give rise to high enantioselectivities in the two sets of transformations: <italic>C</italic><sub>1</sub>‐symmetric monodentate Cu complexes are most suitable for reactions of alkyl‐containing vinylsilanes and bidentate sulfonate‐bridged variants furnish the highest e.r. for substrates with an aryl substituent. Working models that account for the observed trends in selectivity are provided. Utility is demonstrated through application towards a formal enantioselective total synthesis of naturally occurring antibacterial agent bruguierol A.</p> </abstract>