Acylsi lanes

Brook et al. 5X1 observed such reactions during the formation of siienes by photolysis. Using radiation with A > 360 nm, they photolyzed acylsi-lanes such as 127, which bears a mesityl group attached to the carbonyl carbon. On prolonged photolysis of the initially formed silene 128, the C—H bond of the ortho methyl group of the mesityl group added to the silicon-carbon double bond to form the benzocyclobutane 129. Alternatively a 1,5-H shift would lead to the species 130, which would also yield the benzocyclobutane on electrocyclic rearrangement. 

Intermediate 10 turned out to be easily photoisomerizable yielding the stable acylsi-lane 11. According to CCSD(T)/6-31G(d,p)//MP2/6-31G(d,p) calculations23 carbene 10 originates from the initial complex 9. 

Kuwajima et al. developed an efficient route to (Z)-y-siloxyallylmagnesium bromides utilizing the Brook rearrangement of a-silylalkoxides derived from acylsi-lanes and vinylmagnesium bromide [594], Corey et al. recently applied this method to the generation of (Z)-y-siloxyallyllitliiums to achieve rapid syntheses of natural products [595],... 

Oxidation of R CH(OH)SiR3 to R COOH.1 a-Hydroxytrialkylsilanes and acylsi-lanes are oxidized by ozone to the corresponding carboxylic acids, even when one group attached to silicon is an allyl group. 

Homologation of All l Halides. Carbanion (1) serves as an acylsilane anion equivalent in reactions with alkyl halides. The alkylation proceeds smoothly at —40 °C in the presence of HMPA to provide 0,5-acetals which are easily transformed into acylsi-lanes via oxidation with sodium periodate in wet dioxane (eq 8). Acetalization of acylsilanes gives a-trimethylsUyl acetals, which are orthoester synthetic equivalents (eq 9). The synthesis of iso-carbacyclin was achieved by using this procedure. 

The alternative route to (+)-swainsonine by Chen and Tsai used a very similar strategy, but instead formed the indolizidine system by making the C-8/C-8a bond (Scheme 87). In this case the amine 647 and commercially available 2,3-isopropyhdene-D-ribono-1,4-lactone (648) were condensed to form an amide, the terminal diol unit of which was cleaved with lead tetraacetate to give the 5-hydroxypyrroHdinone (—)-649 after acid-promoted cyclization. The thionocarbonate derivative (—)-650 was then treated with iodobenzene bis(trifluoroacetate) to deprotect the acylsi-lane. Intermediate (—)-651 then underwent radical-induced cyclization with tributyltin hydride to give the 8-hydroxyindolizidin-3-one 652 in... 

From this preliminary discussion, the hydrozirconation reaction of alkynes is a valuable process but the scope of functional groups present in the carbon skeleton is rather limited to specific esters. In order to circumvent the limitations, acylsi-lanes were designed as a synthetic equivalent to carbonyl groups. Treatment of 6 with Cp2Zr(H)Cl afforded a 80% yield of the desired olefin 7 with no detectable amount of the carbonyl 1,2-adduct (Scheme 12.9) [13]. 

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