Cyclopentylidene

Acetyloxy)-16,17a-[cyclopentylidene-bis(oxy)]-9-fluoro-llb-hydroxypregna-l,4-diene-3,20-dione. See Amcinomde. 

The cyclopentylidene ketal has also been prepared from dimethoxycyclopen-tane, TsOH, CH3CN, and can be cleaved with 2 1 ACOH/H2O, rt, 2 h. ° Meth-oxycyclopentene (PPTS, CH2CI2, rt, 100%) has also been used to introduce this group." ... 

Acetonide (Isopropylidene), 207 Cyclopentylidene, 215 Cyclohexylidene, 215 Cycloheptylidene, 215 Benzylidene, 217... 

Cyclopentylidene Ketal, i Cyclohexylidene Ketal, ii Cycloheptylidene Ketal, iii... 

The Julia alkene synthesis has been applied to allylsilane synthesis, including the synthesis of 2-cyclopentylidene- and 2-cyclobutylideneethyl(trimethyl)silanes30. 

Since the reactive substructure of cA-2-(l,3-butadienyl)cyclopropylidene is contained in the bicyclic carbene 124, there is a possibility that a carbene-carbene rearrangement occurs together with 1,5-carbon migration. Analysis of the probable reaction pathways allows one to conclude that 1,5-C-migration (124 - 132) in the fixed c -l,3-butadienyl fragment of structure 124 is impossible. The 1,3-carbon migration (124 - 130) which takes place instead is mechanistically analogous to the vihylcyclopropylidene-cyclopentylidene... 

Cyclohexylidene carbene and cyclopentylidene carbene have been generated by the base-induced decomposition of the appropriate 1 -(A-acety 1-jV-nitroso-aminomcthyl)cycloalkan-l-ol in the presence of Aliquat [47-49] and they have been shown to react in high yield with electron rich alkenes (see Section 7.3). Cyclopropylmethylidene, di(cyclopropyl)methylidene, and isopropylidene carbenes have been generated by an analogous route [49]. 

Alkylidene carbenes (isopropylidene [150] cyclohexylidene [150-152] cyclopentylidene [150] cyclopropylethylidene and dicyclopropylmethylidene carbenes [153] and alkenylalkylidene carbenes (Me,C=C=C [154-159] adamantylvinylidene carbene [160] MeCH=CH.CH=C [161] react in good yield... 

Metallacyclopent-l-enes have been obtained by formal [2 + 3] cycloaddition of ethylene to Re(CtBu)(CHtBu)(OR)2 (a carbene/carbyne complex) [612]. Nucleophilic tungsten(II) complexes can react directly with cyclopentanone to yield cyclopentylidene complexes [613]. 

The cascade silylcarbocyclization is applicable to diynals. For example, the reaction of undec-l,6-diyn-ll-al 72 with PhMe2SiH, catalyzed by Rh(acac)(CO)2 affords the corresponding silylated exo-silylmefhylene(hydroxy)bis(cyclopentylidene) 73 (Eq. 20) [48]. 

The reaction of enediyne 74 in which the olefin moiety is located as a part of the cyclo-hexenyl ring proceeds through a cascade SiCaC bicyclization process, followed by /9-hydride elimination, to give tricyclic exo-silylmethylene-bis(cyclopentylidene) 75 in good yield (Eq. 21) [48]. 

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