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Handbook of Functionalized Organometallics Applications in S

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[2+2+1]<br />

R 1<br />

R 1<br />

OH<br />

(CO) 5Cr<br />

R 2<br />

(CO) 5Cr<br />

OMgBr<br />

R 2<br />

R<br />

OMe<br />

OMe<br />

R<br />

+<br />

R 2<br />

11.2 Chromium-Templated Cycloaddition Reactions<br />

OLi<br />

R 1<br />

R 1<br />

(CO) 4Cr<br />

R 1 OH<br />

MeO R<br />

OH<br />

60 61<br />

(CO) 5Cr<br />

Li<br />

C<br />

HCl<br />

R 1<br />

O R<br />

Me<br />

B<br />

OH<br />

R 2<br />

58<br />

R 1<br />

(CO) 4Cr<br />

Li<br />

R 1<br />

O<br />

(CO) 5Cr R<br />

OMe<br />

Li<br />

A<br />

O<br />

R 2<br />

OMgBr<br />

MgBr<br />

R 2<br />

R<br />

OMe<br />

D E<br />

R 2 = H : 59a<br />

R 2 = H: 59b<br />

[2+2+1+1]<br />

OLi<br />

Scheme 11.20 Competition <strong>of</strong> [2+2+1]- vs. [2+2+1+1]cycloaddition.<br />

H<br />

R<br />

OMe<br />

HCl<br />

R 1 OMgBr<br />

R 2<br />

R<br />

OMe<br />

O<br />

Li<br />

F<br />

OMgBr<br />

R 2<br />

R<br />

OMe<br />

results from a [2+2]cyclodimerization <strong>of</strong> a cyclopentadiene <strong>in</strong>termediate orig<strong>in</strong>at<strong>in</strong>g<br />

from 64 via N-quaternization and subsequent H<strong>of</strong>mann elim<strong>in</strong>ation [43].<br />

A unique spirocyclization connect<strong>in</strong>g chromium b-silyl-am<strong>in</strong>ov<strong>in</strong>ylcarbene 70<br />

and 3 equivalents <strong>of</strong> alkyne afforded spiro[4.4]nonatrienes 71 and 72. The formal<br />

[3+2+2+2]cyclization putatively <strong>in</strong>volves an unprecedented triple alkyne <strong>in</strong>sertion<br />

(Scheme 11.22) [46].<br />

465

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