Rearrangement Eschenmoser

Claisen-Eschenmoser rearrangement of 7-hydroxyneopine dimethyl ketal (122), on treatment with MV-dimethylacetamide dimethyl ketal in xylene at... 

In a stereocontrolled route to thromboxane B2, Corey and coworkers used the Eschenmoser rearrangement for the preparation of lactone (91 Scheme 14). The product of the 3,3-sigmatropic shift, amide (90), is directly iodolactonized, thus avoiding often troublesome amide hydrolysis conditions. Another application involving a carbohydrate derivative was demonstrated by Fraser-Reid and coworkers (Scheme 15). Reductive elimination of benzylidene (92), followed by in situ alkylation, Wittig reaction, DIBAL-H reduction and rearrangement, led to amide (94), which was transformed into the corresponding pyranoside diquinane by double radical cyclization. 

As expected, with tertiary allylic alcohol derivatives, the selectivity for the formation of the corresponding trisubstituted alkenes is significantly reduced. Eschenmoser rearrangement of alcohol (281), for example, led in 92% yield to a 7.1 1 ratio of ( )- to (Z)-amides (282) and (283) (Scheme... 

Branched-chain sugars] fromenones, 217 from enopyranosides, 225 from expoxides, 216 Eschenmoser rearrangement, 228, 236, 251... 

GradI, S. N., Kennedy-Smith, J. J., Kim, J., Trauner, D. A practical variant of the Claisen-Eschenmoser rearrangement synthesis of unsaturated morpholine amides. Syn/ett 2002, 411-414. 

The Eschenmoser rearrangement leads to carboxylic amides235 241. The mixed ketene N,0-acetals required as starting materials can be prepared from 1-dimethylamino-l-methoxyethene241 or 1 -dimethylamino-l-methoxypropene242. 

Amide hydrolysis is troublesome with the Eschenmoser rearrangement (for a protocol facilitating the amide hydrolysis see ref 244)245 246, The rearrangements are usually carried out... 

Compound 13 was used to construct the left half of the orally active antifungal agent ambru-ticin319. For a convergent total synthesis of ambruticin via the Eschenmoser rearrangement see ref 320. 

O-Benzylidene-D-allal (20) undergoes Eschenmoser rearrangement to give the unsaturated a-C-hex-2-enopyranoside 23 in 85% yield410. In contrast, treatment of 20 with triethyl orthoacetate and propanoic acid only affords a 1 1 mixture of esters 21 and 22. 

The Eschenmoser rearrangement of 24 has been used in the synthesis of thromboxane B2 from D-glucose413 414. 

Ring opening of 27 by treatment with anilide ion followed by a second Eschenmoser rearrangement leads to 28, a key intermediate in the synthesis of naturally occurring pseudomonic acids, a group of compounds with antimicrobial and antimycoplasmal activity416. 

The Eschenmoser rearrangement of alcohol 3, used in the synthesis of santolinatriene, proceeds with high internal asymmetric induction239,457. The corresponding methyl ester of rearranged product 4 has also been identified as a natural product458. 

In the synthesis of steroid precursors containing a C 5 ethylated side chain, the rearrangement of allylic alcohol 5 via Eschenmoser rearrangement involves both relative and internal asymmetric induction yielding all possible diastereomers459-460. 

Allyl W-phenylimidates rearrange upon heating in refluxing decalin at 190 °C to give ,<5-unsat-urated anilides in moderate diastereoselectivitics, probably due to nonstereoselective formation of the ketene /V,0-acetal intermediates, e.g., formation of 1 and 2250. The diastereoselectivities are opposite to those observed in Vleerwein- Eschenmoser rearrangements (cf. p 3406). Products with a syn relationship predominate in the rearrangement of allyl W-phenylimidates derived from. E-allylic alcohols. 

The sequential 1,2 4,6 rearrangement of 6-benzoyloxy-3-methylcyclohex-2-enol (1, R1 = CH3) and 2,2-diethoxy-4-methyltetrahydrofuran (Table 22, entry 4) and Eschenmoser rearrangement of 4b has been utilized in the synthesis of optically active l/ -[(R)-2-hydroxy-l-methylethyl]-7a/ -methyl-l, 2,3aa,6,7,7a/f-hexahydroindene (6), an intermediate in the syntheses of vitamin D2 and 25-hydroxyvitamin D35155. 

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