25-Alkoxy-26-benzoyloxy derivatives

Structures of this type were generated in the reaction of Af-acyloxy-Af-alkoxyamides with thiols. Treatment of Ai-acetoxy-iV-butoxybenzamide (145, R = Bu, = Me) and a series of Ai-benzoyloxy-Ai-benzyloxybenzamides (139) with cysteine derivatives generated disulfides and hydroxamic esters (Section IV.C.3.b, Scheme 24). The intermediate Ai-alkoxy-Ai-thioalkylamides were unstable under the reaction conditions, reacting with a second thiol molecule at sulfur. The reaction of thiols at the anomeric nitrogen of Af-acyloxy-Ai-alkoxyamides has been modelled theoretically and is predicted to be favourable energetically, leading to a stable substitution product ... 

New possibilities in hetero-Diels-Alder condensation have been opened by the introduction of highly active l-methoxy-3-trimethylsilyloxy-, 4-benzoyloxy-l-methoxy-3-trimethylsilyloxy-, and 2-acetoxy-l-alkoxy-3-trimethylsilyloxy-l,3-butadienes ( Danishefsky dienes, 5). These compounds readily react under atmospheric pressure, in the presence of Lewis acids, with normal aldehydes (e.g., acetaldehyde, benzaldehyde, furfural) to furnish 2,3-disubstituted or 2,3,5-trisubstituted derivatives of 2,3-dihydro-4H-pyran-4-one 7 capable of readily functionalizing to sugars (Scheme 5) [26]. This approach... 

---