Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• Bratislava, Mlynská dolina, Ilkovičova 6, 84215 Bratislava, Slovakia 10.3762/bjoc.15.290 Abstract A range of chiral hydrogen-bond-donating organocatalysts was tested in the Ireland–Claisen rearrangement of silyl ketene acetals. None of these organocatalysts was able to impart any enantioselectivity on the

• rearrangements. Furthermore, these organocatalysts slowed down the Ireland–Claisen rearrangement in comparison to an uncatalyzed reaction. The catalyst-free reaction proceeded well in green solvents or without any solvent. DFT calculations showed that the activation barriers are higher for reactions involving

• rearrangement; silyl ketene acetals; Introduction The Ireland–Claisen rearrangement is a reaction converting allyl esters to γ,δ-unsaturated carboxylic acids. Its key step is a [3,3]-sigmatropic rearrangement of a silyl ketene acetal, which is generated in situ by deprotonation of an allyl ester using a strong

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• to access functionalized alkylidenecyclopropanes, with creation of a new carbon–carbon bond on the three-membered ring with the control of two contiguous stereocenters. Ireland–Claisen rearrangement of cyclopropenylcarbinyl esters The Ireland–Claisen rearrangement of silyl ketene acetals generated

• from allylic (or propargylic) esters is arguably one of the most useful variant of the Claisen rearrangement that has found countless applications in organic synthesis [59]. The feasibility of the Ireland–Claisen rearrangement of cyclopropenylcarbinyl esters was investigated in the case of glycolates

• %). That the Ireland–Claisen rearrangement of cyclopropenylcarbinyl glycolates proceeded with chirality transfer was also verified in the case of alkylidenecyclopropanes 58a and 58i which were obtained with optical purities (ee = 87% and ee = 97%, respectively) identical to those of the corresponding

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• formed as mixtures of (E)- and (Z)-isomers from SF5-substituted acetic acid esters of aliphatic terminal allylic alcohols at low temperature. At slightly elevated temperature, the latter diastereomers are transformed to γ,δ-unsaturated α-pentafluoro-λ6-sulfanyl alkanoic acids in an Ireland–Claisen

• rearrangement [31]. Under slightly modified conditions, this type of rearrangement was also successful for SF5-substituted acetic esters of cinnamyl alcohols [32]. Herein we describe our results [33] of highly syn-diastereoselective silicon Mukaiyama-type aldol reactions of SF5-acetic acid esters with different

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• synthesized in four steps. Esterification with (R)-(+)-citronellic acid (127) yielded a single diastereomer of ester 128. Addition of lithium diisopropylamide to a mixture of 128, trimethylsilyl chloride and triethylamine initiated an Ireland–Claisen rearrangement [63] which gave carboxylic acid 129 in 85

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• framework of B-seco limonoid natural products by means of a [3,3]-sigmatropic rearrangement are described. Detailed model studies reveal, that an Ireland–Claisen rearrangement can be employed to construct the central C9–C10 bond thereby giving access to the B-seco limonoid scaffold. However, application of

• the developed strategy ended up failing in more complex and sterically demanding systems. Keywords: B-seco limonoids; biology oriented synthesis; Ireland–Claisen rearrangement; natural products; tetranortriterpenoids; Introduction B-seco limonoids are a family of more than 100 highly oxygenated

• , depending on the reaction conditions, directly the Claisen rearrangement products was not successful [47]. Alternative strategy: Ireland–Claisen rearrangement. As the Claisen rearrangement precursor, the allyl vinyl ether, could not be obtained under various conditions, we had to change the synthetic