ZnBr2-Catalyzed Insertions of Carbonyl Compounds into Silacyclopropanes: Regiochemical Reversal Dependent on Metal Salt

Abstract

Surprising catalyst‐based regiocontrol: Copper or zinc salts can be employed for the insertion of various carbonyl compounds into silacyclopropanes to afford, respectively, the 1,2‐ and 1,3‐regioisomers of the product with >99:1 regioselectivity (see scheme). Catalysis by ZnBr2 allows access to previously unobserved products. The effects of additives such as H2O, menthol, and di‐tert‐butylpyridine on the regioselectivity of this insertion process are described.

Formation and Utility of Azasilacyclopentadienes Derived from Silacyclopropenes and Nitriles

“…When a 1:1 mixture of acetonitrile and silacyclopropene 1a in C 6 D 6 was treated with 5 mol % of Cu(OTf) 2 , silacyclopropene 1a disappeared over 24 hours, and enamine 2a was formed as a single regioisomer (Scheme 1). Preference for the 1,2-insertion product, which was confirmed by a 1 H- 1 H NOESY experiment, is consistent with the regioselectivity of insertions of carbonyl compounds into silacyclopropenes and silacyclopropanes 2,6. The imine tautomer of 2a was not observed in the product mixure or at any time during the transformation.…”

Silver‐Catalyzed Silylene Transfer

“…74 The combination of these two modifications enabled the isolation of the silacyclopropane product after careful Schlenk filtration. Isolation of the silacyclopropane allowed for either zinc- 64,75 or copper-mediated functionalization of the silacyclopropane to produce 1,2-or 1,3-disubstituted oxasilacyclopentanes. 63 Alternatively, the silacyclopropane could be functionalized in situ through the addition of 30 mol% of zinc bromide (or zinc iodide) and a carbonyl compound to the reaction mixture, which produced oxasilacyclopentane 70 (Scheme 7.12).…”

Silylene Transfer to Allylic Sulfides: Formation of Substituted Silacyclobutanes

“…37 The regiochemistry is in contrast to that observed for analogous zinc-catalyzed carbonyl insertions into silacyclopropanes. 38 The formation of allylic silane 14 from silacyclobutane 3a in the absence of aldehyde supports the existence of transmetalation intermediate 13 (eq 2). The regioselectivity of this reaction is analogous to the copper-mediated transmetalation observed for silacyclopropanes.…”