Cyclopentenones regiospecific

Etiolates 5 and 7, generated regiospecifically by conjugate addition of organocopper reagents to 2-cyclopentenones, can also be stereoselectively alkylated49,50. 

The addition of lithium alkoxydienolates to a,P-enones occurs exclusively in the l,4(a)-mode. For example, alkoxydienolate (202), obtained from ethyl senecioate, adds efficiently, in a tandem conjugate addition-allylation protocol, to cyclopentenone to afford the a,(3-functionalized cyclopentanone (203),153 In contrast, the lithium dienolate (204), from 5-methylbutenolide, affords exclusive y-alkylation,154 b while the analogous phthalide enolates (206) can be exploited to accomplish regiospecific polynuclear aromatic syntheses (Scheme 76).l54c ... 

Cyclopentenone synthesis.2 The key step in a regiospecific synthesis of methylenemycin B (4) involves the reaction of (2-butyne)hexacarbonyldicobalt (1) with tetrahydro-2-(2-propenyloxy)pyrane (2). Although the reaction of complexes... 

The DPM rearrangement has provided a simple route for the construction of the carbon skeleton present in the sesquiterpenoid taylorione, isolated from Mylia taylori [46]. Thus, direct irradiation of the i>cyclopentenone 62 results in efficient, regiospecific DPM reaction affording the r[Pg.177]

Cyclopentenone annelation, The isomeric adducts 1 of 2-methylcyclohexanone and propargyi alcohol both cyclize regiospecifically to the hydrindanone 2 (70%... 

The thermal C3 -> 5 ring expansion of 1-siloxy-l-vinylcyclopropanes occurs either from the Z or from the E isomers. It leads to cyclopentanone silyl enol ethers that are able to undergo either further regiospecific alkylation into 2,3-disubstituted cyclopenta-nones 145.209,213 dehydrosilylation into cyclopentenones The overall process constitutes an efficient three-carbon annelation process (equation 129). 

Regiospecific cyclopentenone annelations vinylsilane-terminated annelations... 

Thia-2-cyclopentenone 30 undergoes regiospecific cycloaddition with 2-methylpropene to provide the cyclobutane derivatives shown in Scheme 10 [55]. 

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