3-cyclopentenol 1 - -1 -alkene

In 1965, Denney et al. (98) reported the reaction of a number of alkenes with ferf-butyl hydroperoxide (TBHP) and cupric salts of chiral acids. The use of ethyl camphorate copper complex 144 in the allylic oxidation of cyclopentene provides, upon reduction of the camphorate ester, the allylic alcohol in low yield and low selectivity, Eq. 82. The initial publication only provided the observed rotation of cyclopentenol, but comparison to subsequent literature values (99) reveals that this reaction proceeds in 12% ee and 43% yield (based on the metal complex). 

Blechert carried out a tandem reaction of enynes in the presence of olefins instead of ethylene (Scheme 21). Treatment of cyclopentenol derivative 58a with Ic in the presence of an alkene affords 59a. The five-membered ring in estrone 58b is cleaved by Ic to give 59 and an alkene part is introduced on the six-membered C ring. However, cycloalkenyl amine derivative 60 is treated in a similar manner in the presence of an allyl alcohol derivative to give pyrrolidine derivative 61, and in this case, an alkene part is introduced on the diene moiety. Presumably, ruthenium carbene complex XVI reacts with an alkyne part to produce the pyrrolidine ring with a regioselectivity opposite to the other cases. 

A concerted bond-forming and bond-breaking process is an alternative to Eq. (m). Methyllithium-TMED in CsHi4, or PhLi in THE does not add to PhCHOHCH=CH2 t-BuLi adds exclusively at the terminal carbon to form PhCH=CHCH2Bu-t and PhCHLiCH(Bu-t)CH2Bu-t. Alkene formation is the dominant reaction with 2-cyclopentenol and 2-cyclohexenol ... 

Silyl-4-alkenals undergo cyclization which gives 3-cyclopentenols. When the intermolecular allylation of enones which favors the conjugate addition pathway is applied to l,8-bis(trimethylsilyl)-2,6-octadiene the four stereocenters of the 2 1 adduct emerge in a defined fashion. ... 

Three-component coupling of alkenes. Larock and Lee10 have reported an efficient one-step intermolccular coupling of three alkenes to form an intermediate (3) to prostaglandins. The starting material is the chiral cyclopentenol 1, which couples with ethyl vinyl ether and l-octen-3-onc (2) in the presence of Pd(OAc)2, NaOAc, and Nal at room temperature to afford the bicyclic enonc 3 in 72% yield as a 2-3 1 mixture of exo- and endo-isomers, which can be readily separated. A number of analogs of this bicyclic system can be prepared by substitution of 2 by other 1-alkenes. Pure ero-3 was... 

Cyclopentenol ethers 78 bearing a quaternary carbon center are formed from the reaction of an alkenylcarbene complex and an alkene. The reaction sequence... 

A modified version of the Simmons-Smith reaction uses dibromomethane and in situ generation of the Cu-Zn couple. Sonication is used in this procedure to promote reaction at the metal surface. Cyclopropanation can also be affected with a combination of CH2I2 and an alkylzinc reagent. The reaction is stereospecific and strongly regioselective. Thus, it has been found that cyclopentenol gives only the mdo-bicyclic alcohol (Scheme 5.34). The mechanism of the Simmons-Smith reaction appears to be carbene transfer from the metal to the alkene without any free carbene being released (Scheme 5.35). 

A reaction called the Johnson polyene cyclization (based on the Stork-Eschenmoser hypothesis) converts triene A into the polycyclic molecule B. When first discovered, an initially formed carbocation at one end of the polyene reacted with a nearby alkene to form a ring containing a new cation. This reacted with another nearby alkene, etc. The reaction was plagued by low yields and formation of polymeric material and decomposition products. This transformation required many years to perfect and two improvements were the use of a cyclopentenol unit on the left to initiate the sequence, which became a cyclopentene unit, and an alkyne unit on the right to end the sequence by generating a methyl ketone. Briefly discuss why these two improvements helped the problems inherent to this reaction. 

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