COMMUNICATION Zinc-Catalyzed Synthesis of Allylsilanes via Si–H Bond Insertion of Vinyl Carbenoids Generated from Cyclopropenes Sergio Mata, Luis A. López,* and Rubén Vicente* Dedication Abstract: Allylsilanes have long been recognized as valuable building blocks for organic synthesis. In this investigation, we report that zinc-catalyzed reaction of cyclopropenes and hydrosilanes represents a convenient route to these versatile unsaturated organosilanes. In this transformation, ZnBr2 serves as an efficient catalyst, allowing the generation of a zinc vinyl carbenoid intermediate, which would be subsequently involved in a Si–H bond insertion. The process shows a broad scope, including the use of substituted and functionalized cyclopropenes or the functionalization of polysiloxanes. Moreover, the zinc-catalyzed carbene insertion into a Ge–H bond is reported for the first time. Organosilanes and siloxanes are widely used as raw chemicals, advanced materials or versatile building blocks in synthetic chemistry. [1] Among them, allylsilanes hold a prevalent position due to an assorted reactivity as alkenes or metal-allyl reagents, among others. [2] Allylsilanes are employed in well-known reactions such as Hiyama [3] or Hosomi-Sakurai reactions, [2,4] and proved useful in complex synthetic targets. [5] Owing to this significance, a variety of methods for the synthesis of allylsilanes have been reported. [6] Among them, metal-catalyzed procedures have emerged as powerful synthetic tools (Scheme 1, top). In particular, transition metal-catalyzed allylic substitutions were found to be very useful. [7] Alternative ways of accessing allylsilanes include palladium-catalyzed silyl-Heck reactions [8] or allene hydrosilylations. [9] Although metal-catalyzed insertions of vinyl carbenes into Si–H bonds would enable the synthesis of allylsilanes, to the best of our knowledge, only stabilized vinyldiazo compounds have been used to access allylsilanes via rhodium(II) vinylcarbenes. [10] Despite these relevant advances, new catalytic methodologies accessing allylsilanes are of great significance. In the course of our studies focused on the development of zinc- catalyzed transformations involving carbenoid intermediates, [11] we recently reported the ZnCl2-catalyzed alkene cyclopropanation through zinc vinyl carbenoids generated from cyclopropenes. [11c,12] Continuing with our interest in the catalytic generation of zinc carbenoids and given the relevance of allylsilanes in organic synthesis, we envisioned that zinc- catalyzed reaction of cyclopropenes with hydrosilanes could represent an appealing synthetic route to these versatile building blocks (Scheme 1, bottom). Very likely, this transformation would involve a zinc vinyl carbenoid intermediate, which would evolve to the final products through a Si–H bond insertion, a certainly underexplored process in zinc carbenoid chemistry. [13] Remarkably, this approach makes use of inexpensive catalysts and reagents avoiding by-product formation. Scheme 1. Common synthetic routes to allylsilanes (top) vs Zinc-catalyzed coupling of cyclopropenes and hydrosilanes (bottom). The feasibility of the planned reaction was tested with 3,3- disubstituted cyclopropene 1a, triethylsilane (2a) and various zinc salts as benchmark substrates (Scheme 2). To our delight, treatment of cyclopropene 1a with an excess of silane 2a (6.0 equiv) and ZnCl2 (10 mol%) (0.1 M, CH2Cl2, rt, 4 h) led to - disubstituted allylsilane 3a (85%, NMR yield), thus supporting our initial hypothesis. Subsequent optimization studies showed that the amount of silane could be diminished (1.5 equiv.) when using ZnBr2 as catalyst at a remarkably low catalyst loading (2 mol%) (0.1 M CH2Cl2, rt, 2 h), providing allylsilane 3a in 85% isolated yield (see the Supporting Information for details on the optimization study). Some salient features of this transformation deserve to be highlighted. First, compared with precious metals typically employed in reactions of cyclopropenes involving carbene species (Au, Ru, Rh), [14] inexpensive and low-toxic zinc salts showed superior efficiency. Besides, zinc catalysts exhibited complementary reactivity to PtCl2, which led to hydrosilylation products as previously reported by Gevorgyan and coworkers. [15] [a] S. Mata, Dr. L. A. López,* Dr. R. Vicente* Departamento de Química Orgánica e Inorgánica e Instituto Universitario de Química Organometálica “Enrique Moles” Universidad de Oviedo c/Julián Clavería 8, 33006-Oviedo (Spain) E-mail: lalg@uniovi.es , vicenteruben@uniovi.es Supporting information for this article is given via a link at the end of the document.