Aluminum Chloride-Catalyzed Intramolecular Allyl-Migration Reaction of Allyl(chloromethyl)silanes and Trapping of the Intermediate with Allyltrimethylsilane

Abstract

Allyl(chloromethyl)diorganosilanes [CH2CHCH2SiR1R2(CH2Cl), R1 = Me, Ph; R2 = Me, Ph, p-ClC6H4] in the presence of aluminum chloride undergo an allyl rearrangement reaction with allylic inversion to afford (3-butenyl)diorganochlorosilanes at room temperature. When allyltrimethylsilane was added to the reactions, the intermediate was trapped to give 1,1-dimethyl-3-(2-trimethylsilylmethyl-4-pentenyl)silacyclopentane (4) along with 3-(butenyl)dimethylchlorosilane in 40% and 18% yields, respectively. The formation of 4 can be explained by the addition reaction of allyltrimethylsilane to 1-silacyclopent-3-yl cation produced by the intramolecular cyclization of (allyl)silylmethyl cation intermediate derived from the interaction of the chloromethyl group with aluminum chloride catalyst, followed by desilylation reaction.

Strategic Applications of the β‐Silicon Effect

“…In all cases, the authors noted a competing allylsilylation pathway, although this was observed to be the minor product regardless of the nature of the starting material, due to the predominance of the intramolecular process. [24] As was initially reported by Hirao in 1981, the βsilicon effect is particularly pronounced in directing the regio chemical outcome in Tsuji-Trost allylic substitutions. [25] This initial report found that a variety of nucleophiles were amenable to the reaction, including several malonates and enamines, with the reaction proceeding well in each case.…”

“…This reaction, catalyzed by AlCl 3 proceeds through the cationic intermediate 41 , which is then either attacked intermolecularly by another equivalent of allyl silane affording 43/44 , or is reattacked by a chloride ion, resulting in the formal allyl migration product 42 as shown in Scheme 9. In all cases, the authors noted a competing allylsilylation pathway, although this was observed to be the minor product regardless of the nature of the starting material, due to the predominance of the intramolecular process [24] …”