Aluminum Chloride Catalyzed Stereoselective [3 + 2] Cycloaddition of Allylsilanes with Simple Conjugated Dienes

Abstract

Allyltrimethylsilane reacts with simple conjugated dienes in the presence of aluminum chloride catalyst to give stereoselective [3 + 2] cycloadducts of trans-vinylcyclopentanes in 29−72% yields at −10 °C. The same reactions give 1,4-allylsilylated compounds as the major products at −50 °C, which cyclize to the annulation products as the reaction mixture is allowed to warm to −10 °C. The reaction using (2-methyl-2-propenyl)trimethylsilane instead of allyltrimethylsilane does not give the annulation due to an unfavorable 1,2-silyl shift but, rather, allylsilylation products. The results are consistent with an initial 1,4-allylsilylation of the conjugated diene, followed by the intramolecular cyclization of the 1,4-allylsilylated alkene to the stereoselective trans-[3 + 2] cycloadduct, via a 1,2-silyl shift.

Lewis Acid-Catalyzed Regio- and Stereoselective Allylsilation of Simple Unsaturated Hydrocarbons

“…The reaction of 4-alkyl-5-silyl-1-pentenes 3b-d, prepared by the allylsilylation of terminal alkenes 2a-c, with 1.2 molar equiv of allylsilanes 1a,b in the presence of anhydrous aluminum chloride and trimethylchlorosilane activator [10][11][12] in organic solvents or neat at 40 o C gave as the major products the unusual allylsilylation products, 2-alkyl-8,8-dimethyl-4-(trimethylsilylmethyl)-8-silanon-1-enes 4a'-d', in addition to polymeric materials. Compounds 4a'-d' are different from the previously reported allylsilylation products, [13][14][15][16] and have a double bond on the carbon with the R 1 group but not on the carbon with R 2 (eq 6).…”

“…A silyl cation or a complex intermediate I is directly formed at the beginning stage of the reaction from aluminum chloride and trimethylchlorosilane, [14][15][16] or from the protodesilylation of allyltrimethylsilane by acids resulting from the reaction of anhydrous aluminum chloride with adventitious water in the reaction mixture. 13,[19][20][21] coming allylsilane, followed by elimination of the trimethylsilyl cation as illustrated in Scheme 1.…”

“…The results are consistent with the formation of silyl cations in these allylsilylations. [13][14][15][16] Equation 8 To confirm that the isomerization had occurred under the allylsilylation reaction conditions, compound 3i was tested using the same reaction conditions but in the absence of 1a. 12% of 3i was converted to give the isomeric product, 3-[3-(trimethylsilyl)propyl]cyclopentene (3i') in 11% yield in 30 min (eq 9).…”

“…This result suggests that s-p interactions in the allylsilylation of diallylsilane are less important than in the allylsilylation of monoallylsilane. [13][14][15][16] …”

“…In analogy to the allylsilylation of alkenes, [13][14][15][16] we have proposed a possible mechanism for the allylsilylation of diallyldimethylsilane (2f) as illustrated in Scheme 3. Intermediate I, generated as described in Scheme 1, adds to one of the allyl groups of 2f to generate a new intermediate II.…”