Cyclopentanol alkene

The reductive coupling/silylation reaction was extended to more complicated polyenes, such as the triene-substituted cyclopentanol 73, which cyclizes to provide 74 with a 72% yield and 6 1 dr after oxidation (Eq. 10) [44], The reaction is chemoselective the initial insertion occurs into the allyl substituent, which then inserts into the less hindered of the two remaining olefins, leaving the most hindered alkene unreacted. 

Hydration of alkenes. This reaction can be effected with oxygen and Co(acac)2 and a secondary alcohol (2-propanol, cyclopentanol). The reactive species is as-... 

Sml2-mediated carbonyl- alkene cyclisations are also effective when the alkene contains a (3-substituent. For example, Enholm reported the Sml2-mediated cyclisation of aldehyde 42 in the presence of MeOH to provide the highly functionalised cyclopentanol 43 containing a quaternary stereocentre, in good yield (Scheme 5.32).62... 

Radical cyclisation-anionic sequences, in which the radical cyclisation involves the addition of a ketyl radical anion to an alkene, are also possible. For example, carbonyl-alkene cyclisation of unsaturated ketone 19 and quenching of the resultant organosamarium with electrophiles allow access to an impressive range of cyclopentanol products (Scheme 6.7).12... 

A better hydrogenation catalyst was generated by reaction of alkene metathesis ruthenium catalyst, with sodium hydride, after the RCM reaction was performed. In that case, hydrogenation can be performed under 1 bar of H2 at 20 °C [86]. Thus, cyclopentanols can be selectively prepared in one pot by RCM of the parents dienes, followed by addition of NaH and hydrogenation [86] (Scheme 40). 

Both disubstituted alkynes (Chapter 3.3, this volume) and isolated terminal double bonds may be reduced by alkali metals in NH3, but isolated double bonds are usually stable to these conditions. However, 16,17-secopregnanes (10 equation 8) afford mixtures of cyclization products (11) and (12) in 61% to 80% yield with Na naphthalenide-THF, Na-NHs-THF, Na-THF or Li-NHs-THF. With Na-NHa-THF-r-butyl alcohol, a 91% yield of a 72 28 mixture of (11) (12) (R = Me) is obtained. This type of radical cyclization of alkenes and alkynes under dissolving metal reduction conditions to form cyclopentanols in the absence of added proton donors is a general reaction, and in other cases it competes with reduction of the carbonyl group. Under the conditions of these reactions which involve brief reaction times, neither competitive reduction of a terminal double bond nor an alkyne was observed. However, al-lenic aldehydes and ketones (13) with Li-NHs-r-butyl alcohol afford no reduction products in which the diene system survives. ... 

Functionalized cyclopentanes. Formal [3-t2]cycloaddition of electron-deficient alkenes with allyldiisopropyl(phenyl)silane gives rise to substituted cyclopentylsilanes. Such products are readily oxidized to cyclopentanols. 

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