Cycloheptatriene silylation

Some interesting reactions have recently been found to occur on heating cycloheptatriene with some organosiliconruthenium carbonyls. An unexpected feature of these reactions is the migration of trimethyl-silyl groups from the metal to the 7r-ligand (R = Me) (17, 74) ... 

Excellent selectivity was observed in the silylation of 1,3,5-cycloheptatriene giving 2-(trimethylsilyl)-l,3,5-cycloheptatriene as the sole product 244... 

Under thermolytic conditions the cycloheptatriene 481 and the silyl enol ether 482 were obtained in 46% and 24% yield, respectively, along with 29% of the unreacted starting compound, the acylpolysilane which is the precursor for the reactive silene (equation 160)". 

In addition to benzene rings, cycloheptatriene is activated or protected by forming the stable if complex 300. An example of the strong stabilization effected by coordination is shown by isolation of the optically active l,3,5-cycloheptatrien-3-ols 301, 304 and 305 as their enol forms. l,3,5-Cycloheptatrien-3-ol was isolated as complex 301 by hydrolysis of silyl enol ether 300. The triene system is stabilized by coordination,... 

The silyl-substituted f/4-cycloheptatriene and -cyclooctatetraene complexes of Fe and U have been investigated to obtain PE spectroscopic information concerning substituent effects on either fluxional behavior or bonding their first ionization potentials are lowered by 0.2 eV247 or remain constant248 with respect to the parent systems. 

Scheme 14 Indanone (146) was converted to alcohol (147). The acetyl derivative of (147) after demethylation was made to react with glyoxal to obtain lactone (149), which reacted with dibromocarbene and diazomethane to yield (150). Its silyl derivative was subjected to ring expansion by radical pathway to obtain cycloheptatriene (151). Its formyl derivative on dehydration gave the natural product lettucenin A.

Xiao and co-workers also revealed an organocatalytie asymmetric CDC reaction of aldehydes with benzylic C—H bonds utilizing chiral diarylprolinol-based silyl ether (Sj-Cl as the eatalyst and DDQ as the oxidant, affording the desired alcohol products 69 in up to 95% ee after the subsequent reduction by NaBH4 (Scheme 2.24). This cooperative system could also be applied to 1,3,5-cycloheptatriene to give the corresponding products in good yields and excellent enantioselectivity. 

Addition of an T -allyl-Fp complex to this compound affords an T -aIlyl-Fp-substituted cycloheptatriene system. Two double bonds are involved in an (T -diene)iron complex. The remaining free double bond of the silyl enol ether attacks as a nucleophile at the cationic r -alkene-Fp moiety to form an (Tj -diene)iron complexed cyclopentane annulated cycloheptadienone. Treatment with CAN in methanol under carbon monoxide atmosphere releases the methoxycarbonyl-substituted free ligand (Scheme 4-25). Reaction of the Ti -dienyliumiron intermediate of Scheme 4-25 with an ( , Z)-isomeric mixture of ri -crotyl-Fp proceeds with high diastereoselectivity. Four new stereogenic centers are formed in the course of this formal [3+2] cycloaddition. A hetero [3+2] cycloaddition is also feasible between T -ailyl-Fp complexes and aromatic aldehydes in the presence of zinc chloride or titanium(IV) chloride to provide tetrahydrofuran derivatives (Scheme 4-26). A 1,2-shift of the iron complex fragment occurs in the course of this reaction. Employment of imines affords the corresponding pyrrolidines. ... 

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