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Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

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C02Me<br />

3.29<br />

NMM<br />

Su-chbmiormate c<strong>of</strong>l0<br />

EW. aiiohydroxamic a&<br />

CBrCI3. hv<br />

Scheme 3.12<br />

Sc hollkopf used a more general approach, reacting the valine derived bis-lac tam<br />

enolate 1.33 (Section 1.3.3.1) with silyl aldehydes. Elimination <strong>and</strong> hydrolysis <strong>of</strong> the<br />

resulting $-hydroxy adducts 3-30 generated a number <strong>of</strong> substituted vinylglycines<br />

(Scheme 3-13)? L-Vinylglycine itself was prepared in 32% overall yield with some<br />

racemization (86% ee).<br />

The D-mannitol derived ddehyde 3.31 <strong>of</strong> Mulzer et aP2 cm be elaborated for<br />

vinylgiycine synthesis. Addition <strong>of</strong> vinyl Grignard reagent followed by a Mitsunobu<br />

reaction with phthdimide on the secondary chiral al1 ylic alcohol <strong>and</strong> subsequent<br />

oxidative cleavage <strong>of</strong> the protected di01 gives D-vinylglycine in approximately 10% yield<br />

from the isopropylidienegl yceraldeh yde with 97% ee (Scheme 3.1 4).<br />

Scheme 3-13

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