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

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366 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

O<br />

O<br />

O<br />

O O<br />

679<br />

O −<br />

N<br />

O<br />

+<br />

336<br />

O O<br />

Ph<br />

O<br />

N<br />

−<br />

+<br />

D14<br />

80ºC, 4 d<br />

Ph<br />

CO 2Me<br />

CO 2Me<br />

D14<br />

80ºC, 4 d<br />

O<br />

Scheme 2.292<br />

O<br />

O Ph<br />

O<br />

O<br />

Ph<br />

N O<br />

77%<br />

ds > 94%<br />

40ºC, 4 h<br />

HN O<br />

678<br />

O<br />

Ph<br />

HCl/MeOH<br />

O<br />

CO2Me<br />

CO 2Me<br />

CO 2Me<br />

CO2Me<br />

71%<br />

N O<br />

CO2Me<br />

O Ph<br />

CO2Me<br />

70%<br />

ds > 91%<br />

40ºC, 4 h<br />

HN O<br />

ent-678<br />

HCl/MeOH<br />

CO2Me<br />

CO2Me<br />

72%<br />

hydrochloride of (−)-(687) . HCl <strong>in</strong> 79% yield. The selective reduction of lactam<br />

(−)-(682) with BH3 . SMe2 <strong>in</strong> THF gave the β-hydroxy ester ( + )-(685) <strong>in</strong> 81%<br />

yield. After esteriÞcation of the alcohol ( + )-(685) with methanesulfonyl chloride<br />

<strong>in</strong> CH2Cl2 <strong>and</strong> subsequent treatment with DBU at 20 ◦ C, the α,β-unsaturated<br />

ester ( + )-(686) was isolated <strong>in</strong> 81% yield. The reduction of ester ( + )-(686) with<br />

DIBALH ((i-Bu)2AlH) <strong>in</strong> CH2Cl2, followed by workup with HCl <strong>in</strong> MeOH,<br />

provided 7a-epi-crotanec<strong>in</strong>e hydrochloride (−)-(688 . HCl) <strong>in</strong> 82% yield (Scheme<br />

2.294).

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