CLAISEN'sche Umlagerungen bei Allyl‐ und Benzylalkoholen mit 1‐Dimethylamino‐1‐methoxy‐äthen

Abstract

Of experiments on the CLAISEN rearrangement of allylic‐ and benzylic‐alcohols with 1‐dimethylamino‐1‐methoxy‐ethylene, communicated earlier in preliminary form, we still owe the description of the experimental details. Here they are.

A study of the Claisen—Eschenmoser reaction for hydroxymethylbenzofurans and-indoles

“…3 It is a considerable partial negative charge in the β position of enamine 14 that makes the rearrangement possible. Although the mechanism of the Claisen-Eschenmoser reaction for various carbinols has not been discussed in detail in the literature, one can assume that a concerted [3,3] sigmatropic rearrangement takes place in standard cases like that observed for 2 (hydroxymethyl)benzofurans 9a-e.…”

“…The Claisen-Eschenmoser reaction of al lylic alcohols with carboxamide acetals, the key step of which is [3,3] sigmatropic rearrangement leading to more complex amides, has been widely described in the litera ture. [1][2][3][4][5][6][7] The representative examples of this transforma tion are the reactions of allylic alcohol 1 2 or 3 hydroxy methyl 1 methyl 2 pyridone (2) 8 with N,N dimethyl acetamide dimethyl acetal (3), which yield N,N dimethyl amides 4 and 5, respectively (Scheme 1).…”

Enantioselective Total Syntheses of Pallambins A–D

“…[7] Chemoselective epoxidation of the electronrich double bond of 13 with m-CPBAgave the corresponding epoxide,w hich was subsequently treated with PTSA in the presence of 1,3-dimethylimidazolidin-2-one (MDI; 18)t o provide the desired allylic alcohol 17. [12] Considering the lactone formation after Claisen rearrangement, the Eschenmoser-Claisen rearrangement of 17 was therefore performed. [12] Considering the lactone formation after Claisen rearrangement, the Eschenmoser-Claisen rearrangement of 17 was therefore performed.…”

“…[11] With ar obust route to 17 established, we focused on the Claisen rearrangement and its variants with different substrates.The Eschenmoser-Claisen rearrangement is known to occur at lower temperatures than other Claisen rearrangements. [12] Considering the lactone formation after Claisen rearrangement, the Eschenmoser-Claisen rearrangement of 17 was therefore performed. Heating 17 and N,N-dimethylacetamide dimethyl acetal in toluene at 115 8 8Ca fforded the desired g,d-unsaturated amide 16 in 88 %y ield as as ingle diastereomer.T he remarkable stereoselectivity can be easily explained by the fact that the Claisen rearrangement should preferentially occur on the less sterically hindered exo face.…”

Enantioselective Synthesis of 3‐ Azabicyclo[4.3.0]nonane Alkaloids

“…Additionally, the stability of the resulting amide further lowers the activation energy of the process, as in the Eschenmoser synthesis of y,d-unsaturated P-silylamides [30], and the rearrangement of 0-allylliminoesters to y,6-unsaturated carboxamides [3 11, however, both of these examples still require high temperatures.…”