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

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RCHO<br />

BocNHOH<br />

R 2<br />

+<br />

+<br />

O N R1 −<br />

PhSO 2Na<br />

H i: BrMg<br />

HO<br />

R<br />

ii: NH4Cl (aq)<br />

52−98%<br />

N<br />

343<br />

Boc<br />

SO 2Ph<br />

2 R ′ -M<br />

M = Li, MgBr<br />

Scheme 2.144<br />

R 2<br />

R 1<br />

N<br />

trans<br />

Method A: CHCl3,Δ ,1 day; method B: 95°C, 15−90 m<strong>in</strong><br />

Scheme 2.145<br />

O<br />

O<br />

R<br />

NITRONE REACTIONS 249<br />

− +<br />

Me<br />

N Boc<br />

+ +<br />

R 2<br />

method A or B,100%<br />

R 1<br />

HO<br />

R<br />

N<br />

N<br />

O<br />

cis<br />

Table 2.11 The isomerization of pyrrolid<strong>in</strong>e N -oxides trans <strong>and</strong> cis at elevated<br />

temperatures.<br />

d.r before Method Method<br />

R 1 R 2 heat<strong>in</strong>g a A d.r. a B d.r. a Yield %<br />

Me Ph 40:60 57:43 98:2 96<br />

Me Me 58:42 83:17 96:4 52<br />

Me Et 50:50 94:6 94:6 94 d<br />

Me i-Pr 67:33 b 96:4 62 e<br />

Me t-Bu 94:6 c 96:4 73<br />

Bn Ph 75:25 c 83:17 95<br />

Ph Ph 93:7 b 95:5 98 d<br />

Cyclohexyl Ph > 98:2 c > 98:2 71 e<br />

a Refers to the ratio of cis / trans -2,5-disubstituted products as determ<strong>in</strong>ed by 400 MHz 1 H NMR<br />

assay (d.r.).<br />

b SigniÞcant decomposition prevented calculation of d.r.<br />

c No 2,5-disubstituted pyrrolid<strong>in</strong>e N -oxides were detected.<br />

d Some decomposition occured on heat<strong>in</strong>g.<br />

e Heat was required to produce fully cyclised material.<br />

Catalytic properties of external chiral additives such as (2 S,3 R)-4-dimethylam<strong>in</strong>o-1,2-diphenyl-3-<br />

methyl-2-butoxide (A16) (574, 575) <strong>and</strong> 2-magnesium-<br />

3-z<strong>in</strong>c salts of dialkyl (R,R)-tartrate (A17) were employed <strong>in</strong> the highly<br />

stereoselective addition of organoz<strong>in</strong>c reagents to derivatives of 3,4-dihydroisoqu<strong>in</strong>ol<strong>in</strong>e-N<br />

-oxide (Scheme 2.147) (576).<br />

−<br />

+<br />

−<br />

Boc<br />

R ′<br />

Me

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