58804-96-9Relevant articles and documents
Silylstannylation of allenes and silylstannylation-cyclization of allenynes. Synthesis of highly functionalized allylstannanes and carbocyclic and heterocyclic compounds
Kumareswaran, Ramaiah,Shin, Seunghoon,Gallou, Isabelle,RajanBabu
, p. 7157 - 7170 (2007/10/03)
Catalyzed by Pd(0), trialkylsilyltrialkylstannane (R3Si- SnR′3) reagents undergo highly selective additions to 1,2-dien-7-ynes and 1,2-dien-8-ynes to give 2-vinylalkylidenecyclopentanes with silicon and tin substituents on the double bonds. Similar additions of distannanes and borostannanes show that the reactions with silylstannanes are superior in terms of ease of handling of the bifunctional reagents and the isolation of the products after the reaction. The chemo- and regioselectivities are controlled by the enhanced reactivity of the allene unit, while the (Z)-geometry of the exocyclic stannylvinylidene is a consequence of the syn-carbometalation and subsequent reductive elimination from Pd with retention of configuration at the vinyl carbon. Synthesis of highly functionalized pyrrolidines and indolizidines and the reluctance of certain kinds of allenynes and silicon-tin reagents to undergo the cyclization illustrate the scope and limitations of the reaction. Based on the isolation of intermediates, a mechanism for the formation of the cyclic compounds is proposed. Model transition states to explain the stereoselectivity in cyclization of substituted allenynes are provided. Further elaboration using the vinyltin and vinylsilane moieties should lead to highly functionalized carbocyclic and heterocyclic compounds. Under similar conditions, addition of silylstannanes to highly functionalized allenes gives E-allylstannanes with high stereoselectivity. Functional groups such as THP- and silyl-ethers, lactones, β- and γ-lactams, α,β-unsaturated esters, olefins, and substituted acetylenes are tolerated under the reaction conditions.
α-ACYLIMINIUM ION-ACETYLENE CYCLISATIONS
Schoemaker, H. E.,Boer-Terpstra, Tj.,Dijkink, J.,Speckamp, W. N.
, p. 143 - 148 (2007/10/02)
Cyclisation of acetylenic ethoxylactams 1b-12b leads to bridgehead nitrogen bicyclic ketones in excellent yields.The reaction is weakly acid-catalysed and proceeds at ambient temperature.The observed regioselectivity effect is discussed in terms of stability of exo vs endo vinyl cations and ring strain effects.The high yield conversion of N-(5-hexynyl)-ethoxy lactams 7b and 8b in the 5/8 and 6/8 fused bicyclic ketolactams 7c and 8c deserves special attention.
