Abstract
Oxygen and nitrogen heterocyclic systems are present in a large number of natural and synthetic compounds. In particular, oxa- and aza-silacyclane, tetrahydrofuran, benzofuran, cycloheptadifuranone, cycloheptadipyrrolone, pyrrolidine, lactone, lactam, phthalan, isochromanone, tetrahydroisoquinolinone, benzoindolizidinone, indoline and indolizidine scaffolds are present in many classes of biologically active molecules. Most of these contain a C=O moiety which can be easily introduced using carbonylative reaction conditions. In this field, intramolecular silylformylation and silylcarbocyclization reactions may afford heterocyclic compounds containing a carbonyl functional group together with a vinylsilane moiety which can be further transformed. Considering these two aspects, in this review a detailed analysis of the literature data regarding the application of silylformylation and silylcarbocyclization reactions to the synthesis of several heterocyclic derivatives is reported.
Highlights
The silylformylation reaction of terminal acetylenic compounds [1,2,3,4,5] consists of the ssiimmuullttaneous introduction of a trialkylsilylggrrouupp and a formyl moiety into a carbon–carbon multippllee bonndd (Schheemmee 1))
Several synthetic applications of silylcarbocyclization reactions have been previously treated as part of more general reviews, focused on the transition metal-promoted cyclizations [68,69,70] or on the chemistry of hydrosilanes with alkynes [27]; a complete and up-to-date overview of SiCAC protocols for the preparation of heterocycles is still missing
Silylcarbocyclization reactions applied to the synthesis of heterocyclic compounds can be divided into three main groups, depending on the starting alkynes: (i) standard silylcarbocyclizations, mainly involving allyl proparyl and dipropargyl ethers/amines, which gave in most cases tetrahydrofuran and pyrrolidine derivatives (Scheme 20, path a); (ii) cascade silylcarbocyclizations, involving instead enediynes and triynes with a suitable chemical structure, which led to the formation of fused tricyclic structures (Scheme 20, path b); (iii) heteroatom-promoted silylcarbocyclizations, involving ethynyl alcohols and amines, where lactones and lactames were obtained (Scheme 20, path c)
Summary
The silylformylation reaction of terminal acetylenic compounds [1,2,3,4,5] consists of the ssiimmuullttaneous introduction of a trialkylsilylggrrouupp and a formyl moiety into a carbon–carbon multippllee bonndd (Schheemmee 1)). Coupling the silylformylation together with the reduction/desilylation step, azasilacyclopentane and cyclohexane were obtained in high yields, as depicted in Scheme 8.
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