09.02.2013 Views

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

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

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

353 b<br />

a<br />

BnO<br />

BnO<br />

354<br />

Bn<br />

N<br />

CHO<br />

OBn<br />

b<br />

74%<br />

NITRONE REACTIONS 257<br />

BnO<br />

HO<br />

BnO<br />

a: TfOMe, MeCN, r.t.; then NaBH 4, MeOH, r.t.; then HgCl 2, MeCN-H 2O, r.t.<br />

b: NaBH4, r.t.<br />

c: 20% Pd(OH)2/C, H2, AcOH, 1 atm., r.t. 18 h; then Dowex (OH − )<br />

−<br />

Scheme 2.154<br />

O<br />

Ph N<br />

HCl<br />

X<br />

CH3OH<br />

X H R<br />

HO N +<br />

R<br />

+ +<br />

Ph<br />

X = NH, O; R = Et, Ph<br />

Scheme 2.155<br />

HO<br />

86%<br />

Bn<br />

N<br />

355<br />

H<br />

N<br />

356<br />

c<br />

R<br />

CH2OH<br />

OBn<br />

OH<br />

X X<br />

Nucleophilic addition of furan to nitrone occurs upon treatment with trimethylsilyl<br />

trißate (TMSOTf) (586, 587). Catalyzed TMSOTf stereoselective addition of<br />

2-[(trimethylsilyl)oxy]furan to chiral nitrones was carried out <strong>in</strong> a short synthesis<br />

of [1S (1α, 2β, 7β, 8α, 8aα)]-1,2-di(t-butyldiphenylsilyloxy)-<strong>in</strong>dolizid<strong>in</strong>e-7,8-diol<br />

(588). Addition to N -gulosyl-C -alkoxymethyl nitrones led to the synthesis of the<br />

core <strong>in</strong>termediate of polyox<strong>in</strong> C (218).<br />

The Þrst example of a nitrone reaction with pyrroles <strong>and</strong> furan <strong>in</strong> the presence<br />

of HCl as an activat<strong>in</strong>g agent was recently reported (589). Depend<strong>in</strong>g on reaction<br />

conditions, these acid-catalyzed reactions make it possible to obta<strong>in</strong> both,<br />

2-heteroaromatic N -benzylhydroxylam<strong>in</strong>es <strong>and</strong> symmetric as well as asymmetric<br />

2,2’-bis -(heteroaryl) alkanes (Scheme 2.155).<br />

OH

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!