Claisen Rearrangements in Carbohydrate Chemistry

Preparation of Sugar Amino Acids by Claisen‐Johnson Rearrangement: Synthesis and Incorporation into Enkephalin Analogues

“…, 126 (37), 85 (100), 69 (14), 55 (27) (2R,3R,6S)-6-Allyloxy-2-[(tert-butyldiphenylsilanyloxy)methyl]-3,6-dihydro-2H-pyran-3-ol (6): tert-Butyldiphenylsilyl chloride (10 mL, 38.61 mmol), Et 3 N (5.86 mL, 42.13 mmol), and DMAP (643 mg, 0.15 mmol) were added to a solution of diol 5 (6.54 g, 35.11 mmol) in dry CH 2 Cl 2 (100 mL) at 0°C under argon. The mixture was stirred overnight and allowed to warm to room temperature.…”

“…[13] Herein we report our re-sults on the design and synthesis of a novel SAA with a 3,6-dihydro-2H-pyran structure (E, Figure 2), using a ClaisenϪJohnson rearrangement as the key step. Although the application of the Claisen rearrangement in carbohydrate chemistry has proven to be a valuable method for the realization of complex synthetic schemes, [14] it has not been used previously for the preparation of SAAs. Additionally, we have incorporated this SAA into Leu-and Met-enkephalin analogues (F).…”

Stereoselective Synthesis of C‐2‐Methylene and C‐2‐Methyl α‐ and β‐C‐Glycosides from 2‐C‐Branched Glycals: Formal Total Synthesis of (–)‐Brevisamide

“…One of the common approaches for the stereoselective formation of C ‐glycosides employs the Claisen or Ireland–Claisen rearrangement8 of glucal‐derived ally vinyl ethers 9. This reaction was extensively studied by using 3‐ O ‐vinyl glycal derivatives to obtain C ‐glycosides of 2,3‐glycals 10.…”

[1,2]- vs [2,3]-Wittig Rearrangement in Carbohydrate Derived Alkenyl Systems

“…T he rearrangement of α-ethereal carbanion, stabilized by phenyl or vinyl, to the corresponding alkoxide known as Wittig rearrangement (WR) is one of the most acceptable methods for the stereoselective formation of a C−C bond. Out of different variants of this classic sigmatropic rearrangement, the [1,2]-and [2,3]-are the most synthetically valuable techniques. The mechanistic investigations reveal that [1,2]-WR involves a radical pair dissociation−recombination mechanism, whereas the [2,3]-WR follows the Woodward− Hoffmann rule that proceeds through a concerted thermally allowed sigmatropic process.…”

“…Out of different variants of this classic sigmatropic rearrangement, the [1,2]-and [2,3]-are the most synthetically valuable techniques. The mechanistic investigations reveal that [1,2]-WR involves a radical pair dissociation−recombination mechanism, whereas the [2,3]-WR follows the Woodward− Hoffmann rule that proceeds through a concerted thermally allowed sigmatropic process. In many such types of rearrangements, the [1,2]-shift competes with the [2,3]-shift to an appreciable extent.…”