Eight-memhered rings,

Eight-memhered Rings with One Nitrogen Atom... 

MiUer SJ, Kim S-H, Chen Z-R, Gruhhs RH. Catalytic Ring-Closing Metathesis of Dienes Application to the Synthesis of Eight-Memhered Rings. J Am Chem Soc. 1995 117(7) 2108-2109. 

Ring contraction (7. 138). Details for the conversion of cyclododecanone (1) to eyeloundecanecarboxylic acid (2) with this reagent are available. With six- to eight-memhered cycloalkanoncs the overall yields are about 75%. In the case of cyclohexadecanonc the overall yield is 68%.2... 

As depicted in ecp (e]-(g). kinetic resolution of u variety of eyelie allylie enters is effected by asymmetric /.r-calaly/edcarhomagncxaiion. Importantly, in addition to six-membered ethers, seven-und eight-membered ring systems can be readily resolved by the Zr-catuly/.ed protocol. It is worthy of note that the powerful Ti-catalyzcd asymmetric epoxidalion procedure of Sharpless 24 is often used in the preparation of optically pure acyclic allylie alcohols through the catalytic kinetic resolution of easily accessible racemic mixtures 25. When the catalytic epoxidalion is applied to cyclic allylie substrates, reaction rates are retarded and lower levels of enantioselectivity are observed. Ru-cataly/ed asymmetric hydrogenation has been employed by Novori to effect resolution of live-and six memhered allylie carbinols 26] in this instance, as with the Ti-cataly/ed procedure, the presence of an unprotected hydroxyl function is... 

In a taxoid synthesis, a cyclocarbonylation is performed with GDI at the 2- and 3-positions of the taxol ring system 925, prior to closure of the eight-memhered B ring, giving 926 in 95% yield [662]. 

This method can he used for a variety of alkenes. The siliranes can he efficiently applied for thermal di-terf-butylsilylene transfer reactions to form other di-terf-hutylsiliranes (8), other thermal and photochemical ring expansion reactions, eg, to diastereoselectively form seven- (6,11), eight- (7), or nine-memhered heterocycles (12). Furthermore the siliranes may he applied to synthesize y-lactones (13), selective synthesis of tiiols, and homoallylic alcohols (14) or stereoselective formation of chiral allylic silanes (15) have also been reported. The following experimental procedure of isonitrile insertions exemplifies the silirane s high reactivity and facile formation of 1,1-di-terf-butyl-iminosilacyclobutanes (1,1-di-tert-butyl-iminosiletans or silacyclobutanimines) (4,5). 

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