Regioselective protection amino alcohols

The Sharpless asymmetric aminohydroxylation [552] of the electron-deficient 2-vinylfuran 469 gives a 7 1 mixture of semi-protected amino-alcohols 470 and 471 (41%). The major product 472 (ee > 86%) was reduced by diisobutylaluminum hydride giving a diol [553] which is then converted into the /3-hydroxyfurylamine derivative 473, an important synthetic building block for various biologically important compounds, including l,5-dideoxy-l,5-imino-alditols such as 474 (O Scheme 110). A less regioselective, but shorter way to intermediate 473 is the direct asymmetric aminohydroxylation of vinylfuran [554,555]. 

The parent 2(3/i/)-oxazolone moiety functions as a bifunctional leaving group when carboxyl groups are activated for acylations and condensations, similar to other five- and six-membered heterocycles such as imidazole, triazole, and 2-pyridinethiol. The excellent leaving ability of a 2(3//)-oxazolone moiety has led to the development of versatile reagents. Thus, 3-acyl- and 3-alkoxycarbonyl-2(3//)-oxazolones serve as ready-to-use -type agents for the regioselective and chemoselective N-protection of amino alcohols, amino phenols and polyamines. 

Silylated cyanohydrins have found considerable utility in the regioselective protection of p-qui-nones, as intermediates for the preparation of 3-amino alcohols and as precursors to acyl anion equivalents. Such compounds are typicdly prepared in high yield by either thermal or Lewis acid catalyzed addition of TMS-CN across the carbonyl group. This cyanosilylation has a variety of disadvantages and modified one-pot cyanosilylation procedures have been reported. - The carbonyl group can be regenerated by treatment with acid, silver fluoride or triethylaluminum hydrofluoride followed by base. ... 

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