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Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

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636 NITRONATES<br />

Table 3.25 Stereochemical outcome of coupl<strong>in</strong>g of nitronates (356) with<br />

nucleophiles (see Table 3.24 <strong>and</strong> Scheme 3.210)<br />

Entry Nitronate<br />

356<br />

R 2 (position) a Tetrahydro<br />

[4H]-<br />

Oxaz<strong>in</strong>es<br />

ConÞguration of<br />

R 1 relatively to<br />

R 2 (position of<br />

R 1 ) a<br />

ConÞguration of<br />

OSi <strong>in</strong> relation<br />

to R 1 (position<br />

of OSi)<br />

1 a Ph (eq) 358a trans (eq) trans (eq) b<br />

2 b Me(eq) 358b trans (eq) trans (eq) b<br />

3 c Ph (eq) 358c trans (eq) trans (eq) c<br />

4 d An (ax) 358 d cis (ax) trans (ax) c<br />

5 e An (eq) 358e cis (eq) trans (eq) b<br />

358e ′ trans (eq) trans (eq) b<br />

6 f OBz (ax) 358f cis (eq) c cis (eq) c<br />

358f ′ trans (eq) trans (eq) b<br />

7 g OCO-C6H4-<br />

NO2-p (ax)<br />

358f ′′ cis (ax) d trans (eq) d<br />

358g cis (eq) d cis (eq) d<br />

358g’ trans (eq) trans (eq) b<br />

358g ′′ cis (ax) c trans (eq) c<br />

8 h H 358h - trans (eq) b<br />

9 i H 358i - trans (eq) b<br />

10 j Ph (eq) 358j trans (eq) c trans (eq) c<br />

11 a Ph (eq) 359a,b trans (eq) trans (eq) b<br />

12 a Ph (eq) 360 trans (eq) trans (eq) b<br />

13 a Ph (eq) 363 trans (eq) c cis (ax) c<br />

14 a Ph (eq) 361 trans (eq) trans (eq) b<br />

aEstablished by NMR.<br />

bEstablished by similarity of NMR data with analogous NMR data of (358c)<br />

cEstablished by X-ray data<br />

dStereochemical assignment for (358f ′′ ) <strong>and</strong> (358g) were based on the close similarity of their<br />

NMR spectral pattern with that of the (358g ′′ ) <strong>and</strong> (358f) respectively.<br />

It should be noted that specially puriÞed <strong>in</strong>dividual stereoisomers of sixmembered<br />

cyclic nitronates were used <strong>in</strong> coupl<strong>in</strong>g with silyl ketene acetal. Hence,<br />

the mechanistic model of the C,C-coupl<strong>in</strong>g reaction can be discussed on the basis<br />

of the conÞgurations of the stereocenters of the start<strong>in</strong>g nitronates of <strong>in</strong>termediate<br />

cations (357) (see Section 3.5.2.1), <strong>and</strong> the result<strong>in</strong>g tetrahydro-oxaz<strong>in</strong>es (358)<br />

(for more details, see below). It should be noted that most of C,C-coupl<strong>in</strong>g reactions<br />

of six-membered cyclic nitronates with silyl ketene acetal are characterized<br />

by a very high diastereoselectivity.<br />

Six-membered cyclic nitronates can be <strong>in</strong>volved <strong>in</strong> C,C-coupl<strong>in</strong>g reactions<br />

with other C-centered nucleophiles hav<strong>in</strong>g high nucleophilicity on Mayr’s scale<br />

(481). This was demonstrated by the reactions of nitronate (356a) (Scheme<br />

3.210).

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