Rearrangements from Tetrahydropyran Derivatives

A sugar derivative related to the purine nucleosides, namely methyl 5-(adenin-l-yl)-5-deoxy-2,3-0-isopropylidene-j8-D-ribofurano-side, is formed by the reaction of methyl 5-amino-5-deoxy-2,3-0-iso-propylidene-jS-D-ribofuranoside with l-benzyl-5-cyano-4[(ethoxy-methylene)amino]imidazole, followed by removal of the benzyl group. On fusion, this compound rearranges to methyl 5-deoxy-2,3-0-isopropylidene-5-[(purin-6-yl)amino]-/8-D-ribofuranoside, which can also be obtained from the reaction of methyl 5-amino-5-deoxy-2,3-0-isopropylidene-/8-D-ribofuranoside with 6-chloro-9-(tetrahydropyran-2-yl)purine. In the same manner, methyl 5-amino-5-deoxy-2,3-di-0-p-tolylsulfonyl-/3-D-ribofuranoside reacts with 6-chloro-9-(tetrahydro-pyran-2-yl)purine to give methyl 5-deoxy-5-[9-(tetrahydropyran-2-yl)-purin-6-yl]amino-2,3-di-0-p-tolylsulfonyl-j8-D-ribofuranoside. With liquid ammonia, 5 -0-p-tolylsulfonyladenosine gives 5 -amino-5 -deoxyadenosine. On heating in p-dioxane, ring closure to 3,5 -an-hydroadenosine is observed. ... 

Ireland demonstrated the usefulness of this reaction in the total s)uithesis of the complex polyether antibiotic, lasalocid A (X537A) [89]. Two Claisen rearrangements were used as key steps for the introduction of the carbon chain to the tetrahydrofuran and tetrahydropyrane rings (arrows indicate the bonds generated by the Claisen rearrangement in Scheme 61). Claisen rearrangement of an oxazole derived from ester of alanine has also been reported (O Scheme 62) [90]. The product was further transformed into C-mannosyl-alanine. 

The versatility of 5-methylene-4-tosyl-3,4,5,6-tetrahydropyran-2-one, derived from the reaction of tert-butyl bromoacetate with dilithiated 2-(tosylmethyl)-2-propen-l-ol and subsequent cyclisation of the 8-hydroxyester with trifluoroacetic acid, is illustrated by its reaction with nucleophiles and acid catalysed rearrangement (94T6603)... 

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