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

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556 NITRONATES<br />

OSiMe2Bu O O<br />

N<br />

t<br />

H<br />

OMe<br />

R 1<br />

OSiMe2Bu t<br />

H<br />

O N<br />

OMe<br />

O<br />

R 2<br />

R 2<br />

R 1<br />

R 1 = Ph<br />

R 2 = H<br />

R 1 = Me<br />

R 2 = CO2Et<br />

MeO<br />

MeO<br />

Scheme 3.134<br />

OSiMe2Bu t<br />

H<br />

H<br />

O N<br />

H<br />

O N<br />

H<br />

OSiMe2Bu t<br />

H<br />

52%<br />

H<br />

76%<br />

O<br />

H<br />

Ph<br />

3S,3aS,4R,4aS,8aR<br />

COMe<br />

CO 2Et<br />

20<br />

[a] D =+134,7<br />

3aS,4R,4aS,8aR<br />

20<br />

[a]D =+75,3<br />

<strong>in</strong>vestigations demonstrated that thia aldehydes (178) exist <strong>in</strong> equilibrium with<br />

isomeric trimers.)<br />

Thio aldehydes (178) <strong>in</strong> situ smoothly react with silyl ether of nitroethane,<br />

<strong>and</strong> regioselectively form cycloadducts (179) as one isomer or as a mixture of<br />

stereoisomers <strong>in</strong> high yields.<br />

This reaction was used as the basis for the development of a procedure for<br />

the synthesis of carbonyl compounds (182) from acetophenone derivatives (180)<br />

(386) (Scheme 3.138).<br />

The process <strong>in</strong>volves one technological step. Tetrabutyl- or triethylammonium<br />

ßuorides can serve as reagents for the cleavage of cycloadducts (181). For this<br />

purpose, N -chlorosucc<strong>in</strong>imide <strong>in</strong> aqueous THF can also be used.<br />

As mentioned above (303) (Scheme 3.90, Eq. 1), bis-trißuoromethyl thioketene<br />

has the deoxygenat<strong>in</strong>g ability toward alkyl nitronates, which is also based on<br />

cycloaddition to the C=S bond.

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