Acylsilanes, synthesis

Ricci, A. and Degl Innocenti, A. (1989). Synthesis and synthetic potential of acylsilanes. Synthesis, 647-660. 

While the preceding sections were written primarily from the point of view of acylsilane synthesis, identical methods have been successfully employed in the synthesis of acylgermanes. 

A different approach toward highly substituted pyrroles involving a one-pot sila-Stetter/Paal-Knorr strategy was realized by Bharadwaj and Scheidt (Scheme 6.182) [343]. In this multicomponent synthesis, catalyzed by a thiazolium salt, an acyl anion conjugate addition reaction of an acylsilane (sila-Stetter) was coupled in situ with the conventional Paal-Knorr approach. Employing microwave conditions at 160 °C for 15 min, the acylsilane was combined with the cx/l-unsaturated ketone in... 

Various nucleophiles other than methanol can be introduced onto the carbonyl carbon. Anodic oxidation of acylsilanes in the presence of allyl alcohol, 2-methyl-2-propanol, water, and methyl /V-methylcarbamate in dichlorometh-ane affords the corresponding esters, carboxylic acid, and amide derivatives (Scheme 24) [16]. Therefore, anodic oxidation provides a useful method for the synthesis of esters and amides under neutral conditions. 

Recently, acylsilanes have been utilized as useful intermediates in organic synthesis [57], For example, treatment of acylsilanes with the fluoride ion generates the corresponding acyl anions which react with electrophiles. On the other hand, by using the electrochemical method, acylsilanes serve as acyl cation equivalents because nucleophiles are introduced at the carbonyl carbon. Chemical oxidation of acylsilanes with hydrogen peroxide which affords the corresponding carboxylic acids has been reported [58], However, the anodic oxidation provides a versatile method for the introduction of various nucleophiles... 

The biomimetic cationic domino cyclization of an acyclic unsaturated substrate to give the tetracyclic scaffold of triterpenes and steroids is intensively described in the literature.1121 The concept has recently been used by Corey et al. to prepare enanti-opure (+)-dammarenediol II 18 in an exceptional short way.1131 The synthesis demonstrates the power of the combination of cation-olefin polyannulation with the aldol cyclization for tetraannulation (scheme 4). Successive treatment of the acylsilane 13 with 2-propenyllithium 14 and the iodoalkane 15 efficiently yidds the epoxytriene 16. The Lewis acid... 

A general synthesis of functionalized 1,2,3-triazolyl acylsilanes (160) was based on the intermolecular cycloaddition of azides 159 with the alkynyl acylsilane 158 (Scheme 9.32) (32). The resulting triazolyl acylsilanes (160) were smoothly converted into their corresponding aldehydes 161 upon treatment with sodium hydroxide in ethanol. 

Oxidation of organoboranes (6, 624 8, 507). A new synthesis of acylsilanes (2) involves oxidation of the hydroboration products of alkynylsilanes (I).1 Oxidation with the commercially available dihydrate of trimethylamine N-oxidc is sluggish however, anhydrous reagent2 is satisfactory for this purpose (equation I). 

Mixed Organofluorine - Organosilicon Chemistry. Part 9. Aldol Reactions of Acylsilanes and (Difluoroenoxy)silanes. Application to the Synthesis of 2-Fluoro 1,3-Diketones ... 

Scheme 12.9. Synthesis of <5-araneosene using DMF = dimethylformamide, TMS = trimethyl-a three-component nucleophilic addition/Brook silyl, Tf = trifluoromethanesulfonyl, rearrangement/alkylation on acylsilanes, by Hu dba = dibenzylideneacetone, dppf = and Corey [30]. TBS = t-butyldimethylsilyl, TAS- 1,1 -bis(diphenylphosphino)ferrocene, DME = F = tris(dimethylamino)sulfur (trimethylsilyl)- 1,2-dimethoxyethane. difluoride, THF = tetrahydrofuran,...

Scheme 12.10. Synthesis of a-onocerin using butyldimethylsilyl, THF = tetrahydrofuran, a three-component nucleophilic addition/Brook Tf = trifluoromethanesulfonyl, DME = 1,2-rearrangement/alkylation on acylsilanes, by dimethoxyethane, TMS = trimethylsilyl, Corey and co-workers [33]. TBS = t- TBAF = n-tetrabutylammonium fluoride.

The dilithio derivative of 1,4-bisphenylsufonylbutane 61 was formed prior to the introduction of homochiral acylsilane 56 into the reaction mixture. The nucleophilic carbonyl addition/Brook rearrangement/elimination sequence delivered bis (fi)-vinyl silyl ether 64 in high yield and with very high selectivity through the putative intermediates 62 and 63. This short and effective synthesis of 55, this time made as the major isomer, was then completed as described above for 54. 

Yanagisawa, A. Habaue, S. Yamamoto, H. Regioselective allylation and propargylation using acylsilanes facile synthesis of PGE3 and F3a methyl ester. Tetrahedron 1992, 48,1969-1980. 

Bulman Page, P.C., Klair, S.S., and Rosenthal, S. (1990). Synthesis and chemistry of acylsilanes. Chemical Society Reviews, 19, 147-195. 

In 2005, Greaney and coworkers applied the PB reaction to the synthesis of merrilactone A (Scheme 7.30) [48]. Very recently, Hammaecher and Portella developed a clean formation of the intramolecular PB reaction of acylsilanes (Scheme 7.31) [49]. 

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