Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Abstract

Trialkyltin hydrides (R 3 SnH) are widely utilized in numerous radical reactions including reductive dehalogenations, [1,2] desulfurizations, [3] and radical cyclizations. [4] Among several R 3 SnH (R Me, Bu, Ph), Bu 3 SnH is the most popular reagent in radical chemistry. The Bu 3 SnH-mediated radical reactions exhibit high regio-and stereoselectivity by changing radical initiators (azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), hn, Et 3 B, etc.) and/or the reaction conditions. [5] Alternatively, such stereoselectivity is also achievable by replacing Bu 3 SnH or Ph 3 SnH [6] with the sterically more hindered (Me 3 Si) 3 SiH. [7] However, it is apparent that there vertically provided uniform wetting of the substrate in the well area and favored heterogeneous film growth. The films prepared by parallel synthesis were shown to have similar morphology to those synthesized under conventional conditions but their X-ray diffraction patterns indicate lesser orientation of crystallites. Parallel synthesis was used to screen the composition space of organic-free clear synthesis solution for ZSM-5 film growth. The composition SiO 2 :(0.5 ± 0.7) NaOH:(1/300 ± 1/700) Al 2 O 3 :80 H 2 O resulted in continuous ZSM-5 films of Si/Al $ 20:1. Experimental SectionTwo types of silicon sources were used: sodium silicate solution (14 % NaOH and 27 % SiO 2 ), and tetraethylorthosilicate (TEOS). Sodium silicate was filtered by using a Buchner funnel with a coarse fritted disc immediately before use. When TEOS was used as the silicon source, it was first dissolved in tetrapropylammonium hydroxide (TPAOH) to form a clear solution of composition TEOS:0.15 TPAOH:0.7 NaOH:98 H 2 O, which was then filtered before use with a PTFE filter (0.45 mm). Tetrapropylammonium bromide (TPABr) solution (25 wt %) was prepared and filtered with 0.45 mm cellulose acetate membranes.The synthesis mixture was prepared by mixing a measured amount of chemicals in a transparent LDPE vial of volume 1 mL (Nalgene). When sodium silicate solution was used, H 2 SO 4 (5 n, VWR) was added to adjust the alkalinity of the final solution. After thorough shaking, a clear synthesis solution was formed and aged for one day at room temperature without stirring before being introduced into the well for reaction. Occasionally, the synthesis mixtures turned turbid immediately after mixing, but the solution became clear after standing for several hours.The substrates employed were nonporous a-alumina disks of diameter 2.5 cm. Prior to seeding the substrates were cleaned by a procedure described in reference [22]. Seeding of the entire substrate surface with a monolayer of silicalite particles was carried out using a previously developed protocol. [12,33] The seeds about 0.4 mm in size were finer than the substrate roughness and did not cause problems in sealing under pressure against the Teflon surfaces.

Molybdenum-Catalyzed Stannylations as Key Steps in Heterocyclic Synthesis

“…A common strategy, suitable for the synthesis of both classes of natural products, is the cyclization of allylic or propargylic ethers of o -iodophenols (yielding benzofuranes) or halogenated benzyl alcohols (providing isochromanes). These cyclizations can be carried out via radical intermediates or in the presence of transition metal catalysts. Propargylic ethers can be cyclized under chromium(II)-mediated nickel(II)-catalyzed conditions or in the presence of palladium catalysts .…”