DANISHEFSKY Silyloxydienes

Danishefsky has extended this methodology for the synthesis of ( )-fucose and( )-daunosamine(85JA1269). Reaction of silyloxydiene 195 with acetaldehyde (197) in the presence of anhydrous zinc chloride gave 90% of a 3.3 1... 

Two homo Diels-Alder reactions and a hetero Diels-Alder reaction, each using a silyloxydiene, have been used in a total synthesis of vinemycinone methyl ester (236) by Danishefsky (84JA2453 85JA1285). Ketoaldehyde 231, prepared by two Diels-Alder cycloadditions, reacted with diene 230 in chloroform in the presence of Eu (fod)j to produce the silyl enol ether... 

Danishefsky has exploited his widely utilized silyloxydiene chemistry to complete a formal total synthesis of 90 (Scheme 1.20). By employing the appropriate oxidation levels for both the diene and dienophile, a resorcinyl ester possessing the required differentiation of the phenolic groups was obtained without further oxidative manipulation. To this end, the dianion of propiolic acid was alkylated with l-bromo-7-octene to give acid 98 in 68% yield. Further alkylation with methyl iodide then gave the ester 99. A Diels-Alder reaction with diene 100, a derivative of methyl acetoacetate, and alkyne 99 then furnished an initial phenolic intermediate which was protected as the benzyl ether to afford... 

Diels-Alder reactions constitute one of the most important methodologies for the constructuction of a cyclic molecular framework. Lanthanide Lewis acid catalyzed Diels-Alder reaction was pioneered by Danishefsky et al., who revealed that NMR shift reagent Eu(hfc)3 served as chiral catalyst in hetero Diels-Alder reaction of silyloxydiene and aldehydes [32]. Later, although Yb(OTf)3 was first introduced for Diels-Alder reactions as an effective catalyst among lanthanide triflates, scandium triflates (Sc(OTf)3), classified as rare earth metal triflate, has gained popularity as a superior catalyst for Diels-Alder reactions [11, 33]. This section highlights several examples of the reactions where lanthanide triflates displayed preferable performance over scandium triflates. 

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