Efficient Synthesis of Clitocine via 1,3-N (endo) to N (exo) Migration: A Revision to Kini’s Work

In the Dimroth rearrangement of heterocycles, often pyrimidines, an exocyclic and a ring substituent are interchanged. However, the term Dimroth rearrangement is frequently used even when there is no knowledge of the reaction mechanism and alternatives are likely. Here, we have employed density functional theory (DFT) calculations at the M06-2X/6-311+G(d,p) level to determine the most plausible rearrangement pathways of 3aminothiocarbonylquinazoline 5, tetrahydrofuranylpyrimidine 21, and 5allyltriazocine 30. For the rearrangement of quinazoline 5 to 9, the [1,3]sigmatropic shift of the thioamido group with an activation barrier of 26.7 kcal/ mol is much preferred over the Dimroth rearrangement (∼46 kcal/mol). An even lower barrier of 21.6 kcal/mol applies to a stepwise [1,3]-shift. The migration of the tetrahydrofuranyl unit in pyrimidines like 21 → 23 can take place by means of a [1,3]-sigmatropic shift with a low barrier (≤17.5 kcal/mol) rather than a Dimroth rearrangement under acidic conditions and most likely also under neutral conditions (∼30 kcal/mol). In the rearrangement of 5-allyl-6-iminotriazocine 30 to 32, the [3,3]-sigmatropic shift (aza-Cope rearrangement) is preferred over the Dimroth mechanism under neutral conditions, but in the presence of acid, the azonia-Cope rearrangement of an allyl group and the true Dimroth rearrangement have comparable activation energies.

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Unexpected Observation of the Dimroth Rearrangement in the Ribosylation of 4-Aminopyrimidines

Baiazitov

Sydorenko

Ren

et al. 2017

J. Org. Chem.

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A method for the preparation of 1-(N-ribofuranosyl)-6-imino-1,6-dihydropyrimidin-4-amines 3 or 4-(N-ribofuranosyl)-6-aminopyrimidines 4 via glycosylation of 4-aminopyrimidines 2 or 5 is described. Silylated 4-aminopyrimidines 2 or 5 upon ribosylation with 1 provide products 3. When intermediates 3 contain a strongly electron-withdrawing group, such as C(4)-Cl or C(5)-NO, they rearrange to products 4 in the presence of aqueous ammonia. A mechanism is proposed that involves a ring-opening/ring-closing (Dimroth) rearrangement.

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Efficient Synthesis of Clitocine via 1,3-N (endo) to N (exo) Migration: A Revision to Kini’s Work

Cited by 3 publications

References 2 publications

Synthesis of Thiadiazolylaminoglycosides Through Ring Contraction of Triazinoglycosides Induced by [TBA‐Ox]

Synthesis of Thiadiazolylaminoglycosides Through Ring Contraction of Triazinoglycosides Induced by [TBA‐Ox]

When a “Dimroth Rearrangement” Is Not a Dimroth Rearrangement

Unexpected Observation of the Dimroth Rearrangement in the Ribosylation of 4-Aminopyrimidines

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