Desilylative ring-opening

Under basic conditions, methanol added to methyl 2-(trimethylsiloxy)-2-vinylcyclopropane-carboxylate (15) via desilylation, ring opening and formation of an a,j6-unsaturated ketone moiety. 

In the presence of TiCh, trimethylsilylmethylated cydopropyl ketone 150 undergoes desilylative ring-opening reaction to generate (Z)-enolate 151, which then reacts with dnnamaldehyde, giving rise to syn-adduct 152 stereoselectively (Scheme 5.38) [55]. 

Synthetic work commenced with evaluation of an azomethine ylide dipole for the proposed intramolecular dipolar cycloaddition. A number of methods exist for the preparation of azomethine ylides, including, inter alia, transformations based on fluoride-mediated desilylation of a-silyliminium species, electrocyclic ring opening of aziridines, and tautomerization of a-amino acid ester imines [37]. In particular, the fluoride-mediated desilylation of a-silyliminium species, first reported by Vedejs in 1979 [38], is among the most widely used methods for the generation of non-stabilized azomethine ylides (Scheme 1.6). 

The ring-opening of the cyclopropane nitrosourea 233 with silver trifiate followed by stereospecific [4 + 2] cycloaddition yields 234 [129]. (Scheme 93) Oxovanadium(V) compounds, VO(OR)X2, are revealed to be Lewis acids with one-electron oxidation capability. These properties permit versatile oxidative transformations of carbonyl and organosilicon compounds as exemplified by ring-opening oxygenation of cyclic ketones [130], dehydrogenative aroma-tization of 2-eyclohexen-l-ones [131], allylic oxidation of oc,/ -unsaturated carbonyl compounds [132], decarboxylative oxidation of a-amino acids [133], oxidative desilylation of silyl enol ethers [134], allylic silanes, and benzylic silanes [135]. 

MoC15 promotes the ring-opening transformations of cyclopropyl ketones. Cyclopropyl phenyl ketone 251 is converted to 1-phenyl-1,2,4-trichloro-1-butene 252. Desilylative lactonization of propyl 2-(trimethylsilylmethyl)cyclo-propanecarboxylate 253 yields ds-2-chloro-4-pentanolide 254 stereoselectively [144]. (Scheme 100)... 

In the first step, Ag+ promotes the departure of Cl- to give a cyclopropyl carbocation. This undergoes two-electron disrotatory electrocyclic ring opening to give the chloroallylic cation, in which the empty orbital is localized on Cl and C3. Then 09 can add to C3 desilylation then gives the product. 

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

Reductive y-lactone ring opening, with concomitant desilylation at the tertiary position by LiAlH4, gave triol 17 in 80% yield. Finally, acetonide formation followed by oxidation with tetra-n-propylammonium perruthenate/A-methylmorpholine / /-oxide oxidation, led to the target aldehyde 19 in 80% overall yield. 

Similar to these results, but accompanied with ring opening, are the desilylation reactions of substituted aziridines. Treatment with cesium fluoride (1 equiv.) in HMPA (tetrabutylammonium fluoride in THF or DME gives lower yields) at room temperature followed by aqueous work-up, yields desilylated open-chain compounds.320... 

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