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Handbook of Functionalized Organometallics Applications in S

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TBSO<br />

390<br />

9 Polyfunctional Organocopper Reagents for Organic Synthesis<br />

reoisomer. Furthermore, the reaction can be carried out us<strong>in</strong>g catalytic amounts<br />

<strong>of</strong> copper salts (Scheme 9.17) [28].<br />

Behl<strong>in</strong>g and Lipshutz found a method for generat<strong>in</strong>g higher-order cyanocuprates<br />

such as 66 directly from v<strong>in</strong>ylzirconium <strong>in</strong>termediates. This method was<br />

successfully applied to the synthesis <strong>of</strong> misoprostol, a commercially available prostagland<strong>in</strong><br />

antiulcer drug. The synthesis starts with the hydrozirconation <strong>of</strong> an<br />

alkyne such as 67 us<strong>in</strong>g Schwartz reagent. Transmetallation <strong>of</strong> the alkenylzirco-<br />

1) Me 3Al, Cp 2ZrCl 2<br />

ClCH 2CH 2Cl,<br />

0 ºC tort,3h<br />

CH3 2) Bu CuLi·LiCN<br />

2<br />

THF, -23 ºC, 5 m<strong>in</strong><br />

2) Bu CuLi·LiCN<br />

2<br />

THF, -23 ºC, 5 m<strong>in</strong><br />

Bu<br />

TBSO<br />

H 3C<br />

H 3C<br />

65 61<br />

1) DIBAL-H<br />

hexane, 0 to 50 ºC, 2h<br />

Scheme 9.17 Zr/Cu-exchange reactions.<br />

Me<br />

67<br />

Et 3SiO<br />

Bu<br />

OSiMe 3<br />

Me 3SiO<br />

Me<br />

O<br />

1) Cp2Zr(H)Cl 2) n-BuLi (2 equiv)<br />

3) CuCN·MeLi<br />

Bu<br />

Bu<br />

(CH 2) 6CO 2Me<br />

Scheme 9.18 Synthesis <strong>of</strong> protected misoprostol.<br />

O<br />

63<br />

Me<br />

Li<br />

Cu<br />

Li<br />

OSiMe 3<br />

66<br />

Cu<br />

Bu<br />

Me<br />

Cu(CN)Li2 (CH 2) 6CO 2Me<br />

OSiEt 3<br />

O<br />

-23 ºC,<br />

30 m<strong>in</strong><br />

O<br />

-23 ºC,<br />

30 m<strong>in</strong><br />

O<br />

H 3C<br />

62: 92%<br />

O<br />

64:75 %<br />

OTBS<br />

CH 3

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