Silicon heterocycles, unsaturated, synthesis

Reactions of silylenes with unsaturated organic substrates are valuable for the synthesis of novel silicon compounds (1,2). Over the past three decades, the reactions of silylenes with carbonyl compounds have been extensively investigated (3—5). It has been shown that these reactions produce diverse types of products via siloxirane or carbonyl silaylide intermediates while the carbonyl C—O a bond is generally maintained (3—5). Complete cleavage of the C—O bond has only been observed in several cases (4). Furthermore, the synthesis and physical properties of siloles and related unsaturated carbon—silicon heterocycles are of great interest as heteroaromatic molecular precursors and potential molecular optical materials (6). In this experiment, reaction of a NHC-stabilized silacyclopentadienylidene (silole silylene) with aldehydes, leading to the formation of the novel NHC-stabilized a,(3-unsaturated silanone, was described. 

The donor-stahilized hydrosilanimine is potentially useful as a hydrosilylation reagent. In addition, the existence of the Si=N double bond allows the cycloaddition reactions with unsaturated organic molecules for the synthesis of silicon heterocycles. 

Intramolecular [3+2] cycloaddition reactions of unsaturated diazocarbonyl compounds as well as transition-metal-catalyzed intramolecular carbene-type reactions of diazo compounds constitute an important strategy in contemporary synthesis of alicyclic and heterocyclic systems [1]. In a program directed towards the synthesis of silaheterocycles according to this concept, we have used various silicon-functionalized (silyl)diazoacetates [2] as starting materials. In this communication, we report on the synthesis of silaheterocycles from a-(alkynyloxy)silyl-a-diazoacetates [3], which can be prepared easily by successive reaction of a silyl bis(triflate) with an alkyl diazoacetate and a propargyl alcohol [4],... 

The aim of this Report is to review new methodology for the synthesis of saturated heterocyclic compounds. Emphasis is placed on reactions which involve a cyclization step and few ring transformations are described. Heterocycles which contain phosphorus, selenium, and silicon as the heteroatom are omitted. A few key steps in complex natural product syntheses are mentioned, but carbohydrates are excluded. The rapidly increasing numbers of reports describing the synthesis of saturated and unsaturated lactones and of crown ethers are covered in Chapters 3 and 10. 

The reaction products represent the first examples of silicon analogs of the ubiquitous enone and dienone compounds, which are potentially useful for the synthesis of novel unsaturated silicon—carbon heterocycles. 

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