Cyclopentanone synthesis

Whereas lactone annulation invokes a relief of strain of the four membered ring by migration of the ring bond to an electron deficient oxygen, a similar migration to an election deficient carbon creates a cyclopentanone synthesis (Eq. 73). The release of approximately 84 kJ/mole (20 kcal/mole) provides a strong driving force. Thus, the 1,1-cyclobutanone annulation of ketones translates into a 1,1-cyclopentanone annulation. 

CYCLOPENTANONE SYNTHESIS BY INTRAMOLECULAR ACYLATION OF 5-TRIMETHYLSILYLALKANOYL CHLORIDES"... 

Cyclopentanes, synthesis, 66, 10 CYCLOPENTANONE SYNTHESIS, 66, 87, 92, 93 Cyclopentanone, 2-carbomethoxy-3-vinyl, 66, 56 Cyclopentanone, 2-ethenyl-2-methyl (88729-76-4), 66, 94 2-CYCL0PENTEN-1 -ONE, 3-METHYL-2-PENTYL-, 65, 26 Cyclopropane, 1-trimethylsilyloxy-l-ethoxy-, 66, 44 Cyclopropanecarboxylic acid chloride, 66, 176... 

Cyclopentanone synthesis. The palladium reagent (I), as well as tetrakis(tri-phenylphosphine)palladium, promotes a 1,3-alkyl shift from oxygen to carbon with no allylic inversion. Two typical examples are formulated.1... 

Replacing the carboethoxy group by a thiophenyl group in the cyclopropyltriphenyl-phosphonium salt generates a new synthon 373 which is useful in cyclopentanone synthesis ... 

B. M. Trost and T. A. Runge, Pd-catalyzed 1,3-oxygen-to-carbon alkyl shifts A cyclopentanone synthesis, J. Am. Chem. Soc. 703 7559 (1981). 

Carbohydrate-derived furanoid pentenals can also be used in rhodium-catalyzed stereoselective cyclopentanone synthesis via hydroacylation81. 

Cyclopentanone synthesis via [2+2 + 1] cycloaddition of two alkenes and carbon monoxide ... 

This radical can be quenched by tin hydride, but still is able to undergo tandem C-C bond-forming reactions if a rationally designed system follows. However, as summarized in Scheme 6, tandem sequences have to overcome the problem of isomerization to the thermodynamically more stable six-membered radical [26], Table 2 lists several examples of cyclopentanone synthesis based on a 4+1 radical annu-lation process. The first example shown in Table 2 demonstrates that the 4-hexenyl radical/CO system faces this isomerization problem, which is difficult to suppress [27, 26a]. Of course, some substituents, such as phenyl and alkoxycarbonyl groups, are effective in hindering such an isomerization process from 5 to 6 (runs 2, 3, 4) [27]. 

Oxime ethers and imines are viable intramolecular radical acceptors. Advanced precursors of (—)-tetrodotoxin were prepared via radical cyclization reactions using oxime ethers as radical acceptors [105]. In the synthesis of (+)-7-deoxypancratistatin (160) [106] (Scheme 55), the intermediate 159 was prepared via tandem radical cyc-lizations of the precursor 158 possessing an A -aziridinylimine and an 0-benzyloxime moiety. Direct formation of lactones is possible as shown in the reaction of the (2,2-diphenylhydrazono)acetate 161, which afforded the hydrazino lactone 162 along with the epimer 163. (-t-)-Furanomycin (164) was synthesized from 162 [107] (Scheme 56). Normally, use of nitrile radical acceptors is limited to cyclopentanone synthesis, but the rigidity of the 1,6-anhydro scaffolding in the bromide 166 enabled radical cyclization to give the tricyclic ketone 167, which comprises the entire skeletal framework of tetrodotoxin [108] (Scheme 57). 

Cyclopeutanoues, Jung and Hudspeth have devised a new cyclopentanone synthesis by three-carbon annelation of an alkene via a Diels-Alder reaction. They chose the dimethoxytetrachlorocyclopentadiene 1 as the diene component because it is remarkably reactive. The general method is outlined for methyl acrylate (2, equation I). The chlorine atoms of the adduct 3 are replaced by... 

Asoaka, M., S. Hayashibe, S. Sonoda, and H. Takei Synthesis and Utilization of Optically Active 2-Substituted 4-(Trimethylsilyl)cyclopentanones Synthesis of (—)-Massoialactone and (-l-)-P-Cuparenone. Tetrahedron Letters, 31, 4761 (1990). 

Further examples of the palladium-catalysed l,3-(oxygen-to-carbon) rearrangement in allyl vinyl ethers have been noted. Detailed mechanistic and stereochemical considerations have lead to a clear picture of how these reactions can be used in cyclopentanone synthesis. The reaction nicely complements the normal thermal [3.3]rearrangement of allyl vinyl ethers. 

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