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Handbook of Functionalized Organometallics Applications in S

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414<br />

10 Functional Organonickel Reagents<br />

MeO<br />

+ O N O<br />

Ni(COD) 2/PPh3 1,2-dichloroethane<br />

Ph<br />

69% (5:1)<br />

MeO<br />

Oxa and aza-benzonormornadienes undergo [2 + 2] cycloaddition with alkynes<br />

<strong>in</strong> the presence <strong>of</strong> NiCl 2(PPh 3) 2,Ph 3P and Zn powder <strong>in</strong> toluene to afford the correspond<strong>in</strong>g<br />

exo-cyclobutene derivatives <strong>in</strong> fair to excellent yields [116,117].<br />

MeO<br />

OMe<br />

O<br />

10.5.2<br />

[4+2] Cycloaddition<br />

+ Ph CH(OEt) 2<br />

NiCl 2(PPh 3) 2<br />

PPh 3<br />

96%<br />

MeO<br />

OMe<br />

O<br />

O<br />

O<br />

N<br />

Ph<br />

Ph<br />

CHO<br />

The nickel(0)-catalyzed stereoselective <strong>in</strong>tramolecular [4 + 2] cycloaddition between<br />

dienes and unactivated allenes or alkynes has been shown to be an efficient<br />

complement to the uncatalyzed concerted Diels±Alder reaction that <strong>of</strong>ten requires<br />

stereoelectronic restrictions. In a typical reaction,treatment <strong>of</strong> dienyne with<br />

10 mol% Ni(COD) 2 and 30 mol% <strong>of</strong> tri-o-biphenyl phosphite at room temperature<br />

TMS<br />

TMS<br />

Ni(acac) 2/Et2AlOEt P(O-iC3HF6) 3<br />

H<br />

TMS<br />

O<br />

Ni(COD) 2/P(O-iC3HF6) 3<br />

N<br />

Me<br />

81%<br />

TMS N<br />

Me<br />

Ni(COD) 2/P(O-o-BiPh) 3<br />

97%<br />

[Rh(COD)Cl] 2/P(O-o-BiPh) 3<br />

90%<br />

H<br />

H<br />

Me<br />

OTBS<br />

OTBS<br />

O

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