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

DMF, Nal
O * BocH
Vm O
Scheme 2.20
The aldehyde was also generated using the Dess-Martin periodinaneS3 2.48,
synthesized by a siight modification of the method described by Ireland." Aithough
Schreiber and coworkers described acceleration of the Dess-Martin oxidation when
performed in the presence of water," it was imperative that the reaction be executed
under anhydrous conditions due to the sensitivity of the ortho ester to acid hydrolysis.
Results initially varied considerably from batch to batch of the periodinane 2.48, with
sorne batches fading to give the desired aldehyde 2.46 although oxidation of benzyl
alcohol proceeded successiùlly. We detemiined that residuai acetic acid, from the
acetylation reaction to give the periodinane 2.48, was opening the ring of the ortho ester
and hence a complex mixture of products. Washing of 2.4û with large volumes of
anhydrous diethyl ether under Nz in a Schlenk tube gave 2.48 with consistent punty for
the synthesis of aldehyde 2.46. An advantage of this method of oxidizing the alcohol is
that the reaction is performed at raom temperature, although the synthesis of 2.48