Allylsilane-terminated reactions

Scheme 6/1.3. Allylsilane-terminated domino Heck reactions of 6/1-14a-f.

Scheme 6. Allylsilane-terminated cascade Heck reaction by Tietze et al.

Reaction Scope Allylsilane-Terminated Enantioselective Cyclizations... 

Scheme 12.19 Allylsilane terminated enantioselective intramolecular Mizoroki-Heck reactions.

Barbero A, Castreno P, Garcia C, Pulido FJ. Intramolecular cyclization of tcrt-butyldiphenylallylsilane units and carbonyl groups allylsilane terminated cyclization versus the ene reaction. J. Org. Chem. 2001 66 7723-7728. 

A subsequent publication by Blechert and co-workers demonstrated that the molybdenum alkylidene 3 and the ruthenium benzylidene 17 were also active catalysts for ring-opening cross-metathesis reactions [50]. Norbornene and 7-oxanorbornene derivatives underwent selective ring-opening cross-metathesis with a variety of terminal acyclic alkenes including acrylonitrile, an allylsilane, an allyl stannane and allyl cyanide (for example Eq. 34). 

Only recently a selective crossed metathesis between terminal alkenes and terminal alkynes has been described using the same catalyst.6 Allyltrimethylsilane proved to be a suitable alkene component for this reaction. Therefore, the concept of immobilizing terminal olefins onto polymer-supported allylsilane was extended to the binding of terminal alkynes. A series of structurally diverse terminal alkynes was reacted with 1 in the presence of catalytic amounts of Ru.7 The resulting polymer-bound dienes 3 are subject to protodesilylation (1.5% TFA) via a conjugate mechanism resulting in the formation of products of type 6 (Table 13.3). Mixtures of E- and Z-isomers (E/Z = 8 1 -1 1) are formed. The identity of the dominating E-isomer was established by NOE analysis. 

The ruthenium-catalyzed addition of C-H bonds in aromatic ketones to olefins can be applied to a variety of ketones, for example acetophenones, naphthyl ketones, and heteroaromatic ketones. Representative examples are shown in the Table 1. Terminal olefins such as vinylsilanes, allylsilanes, styrenes, tert-butylethy-lene, and 1-hexene are applicable to this C-H/olefin coupling reaction. Some internal olefins, for example cyclopentene and norbornene are effective in this alkylation. The reaction of 2-acetonaphthone 1 provides the 1-alkylation product 2 selectively. Alkylations of heteroaromatic ketones such as acyl thiophenes 3, acyl furans, and acyl pyrroles proceed with high yields. In the reaction of di- and tri-substitued aromatic ketones such as 4, which have two different ortho positions, C-C bond formation occurs at the less congested ortho position. Interestingly, in the reaction of m-methoxy- and m-fluoroacetophenones C-C bond formation occurs at the congested ortho position (2 -position). 

The 1,5-diketone formation by the Michael addition of allylsilane (48) to a, -unsaturated ketones was applied to the synthesis of (+)-nootkatone. Reaction of the keto group of keto aldehyde (58) with allyl Orignard reagent and dehydration gave the diene aldehyde (59). The selective oxidation of the terminal double bond afforded the 1,5-dica nyl compound (60), which is not stable and converted directly to pyridines and phenols (Scheme 18). ... 

Poor yields were observed initiating the reaction by epoxide ring opening107. A steroidal skeleton was prepared using allylsilane for 5-exo cyclization in the termination step. Both induction and termination are not stereospecific and a mixture of diastereomers is isolated in modest yield93. 

Borylation at the terminal -carbon atom of allylsilanes with bis(pinacolato)diboron furnishes a valuable reagent for homologation and/or functionalization by two different reactions. ... 

The reactions of TMSCu are in marked contrast to the reactions of trimethylsilyllithium with similar substrates. Whereas treatment of a l-chloro-2-alkene with TMSCu affords a 3-trimethylsilyl-l-alkene, reaction of TMSLi with these same starting materials yields terminal ( )-aUylsilanes where the stereochemistry of the double bond is retained in the product (eq 7). Thus a single allylic halide yields either of two regioisomers by proper choice of reaction conditions. With aUyUc phosphates, TMSCu affords as major product the aUylsUane resulting from attack by what is formally an SN2 -like reaction. With TMSLi, however, the major product is always the isomeric allylsilane having a more substituted internal double bond (eq 8). 

An impressively short synthesis of (—)-epimyrtine (1098) by Martin and coworkers featured an iminium ion cycUzation cascade initiated by reaction between the monoprotected dialdehyde 1139 and the optically active amine-substituted allylsilane (R)-1140, and terminated by the addition of... 

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