Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• site providing a trans relationship between the hydroxy and the phosphine substituents. Keywords: isopinocamphone; monoterpenes; phosphines; [2,3]-sigmatropic rearrangement; verbanone; Introduction Chiral phosphorus compounds, despite many years of research, still enjoy unflagging interest of many

• [2,3]-sigmatropic rearrangement of an allylic diphenylphosphinite to the diphenylphosphine oxide (Scheme 4) [16]. Diphenylphosphinite 19 was formed in the reaction of allylic alcohol 6 with diphenylphosphine chloride in the presence of DMAP at −20 ºC. The temperature was raised to induce phosphinite’s

• [2,3]-sigmatropic rearrangement (20) as shown in Scheme 4. The reaction progress, conversion of 19 into 21, was monitored by 31P NMR (ROPPh2 δ = 113 ppm; RP(O)Ph2 δ = 30 ppm). The phosphinite 19 disappeared after 48 h at 100 °C. The product was crystallized from heptane to give phosphine oxide 21 in 92

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• butenolide 70. The second one is the reaction of alicyclic alcohol 73 with dimethylformamide dimethylacetal to give an allylic amide by means of a [2,3]-sigmatropic rearrangement of a carbene intermediate. Epoxidation the allylic amide with m-CPBA gave 74, followed by lithium hexamethyldisilazide-induced β

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

• ]. In this review, we shall exclusively focus on alternative strategies that rely either on a [2,3]-sigmatropic rearrangement (Scheme 1, reaction 4) or a [3,3]-sigmatropic rearrangement of cyclopropenylcarbinol derivatives (Scheme 1, reaction 5). These transformations have emerged as useful tools over

• to enantiomerically enriched cyclopropenylcarbinols [31], Marek et al. investigated other classes of transformations involving those latter strained analogs of allylic alcohols as substrates. In 2007, the [2,3]-sigmatropic rearrangement of cyclopropenylcarbinyl phosphinites was reported as a route to

• [2,3]-sigmatropic rearrangement of the in situ-generated phosphinites 2a–h. Primary or tertiary cyclopropenylcarbinols reacted equally well, as shown with the formation of phosphine oxides 3a (94%), 3b (93%) and 3c (87%). The [2,3]-sigmatropic rearrangement of phosphinites 2d–h derived from secondary

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• would be the attack of triflinate as O-nucleophile at the cyclohexane carbon, followed by [2,3]-sigmatropic rearrangement [31]. Conclusion With the synthesis of the [8.4.0]bicycles 18 and 19 that contain a 1,3-cyclohexadiene partial structure, we have made progress towards the synthesis of a small group

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

• acetylide to the carbonyl group of 69, followed by desilylation under basic conditions gave rise to (±)-ethynylcarbinol, which was separated by chiral HPLC. The desired diastereomer was then transformed to benzene sulfinate ester 70. A palladium-catalyzed [2,3]-sigmatropic rearrangement formed an isomeric

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• cascade approach for rapid access to tetracene sulfoxides in 2007 (Scheme 1). In 2012 Liu used a Pd-based strategy to provide 12-substituted 5-aryltetracenes [after final trapping with RB(OH)2)] [16]. Both of these reactions rely on the formation of bis-allenes 2, attained by Lin through 2,3-sigmatropic

• rearrangement of 1a [14] or by SN2’ carbonate displacement in 1b by Pd0(PPh3)2 in Liu’s case [16]. To circumvent reversibility of these pericyclic annulation strategies Lin relied on PhSOH elimination while Liu relied on ubiquitous palladium β-hydride steps leading to tetracenes 3 and 4. We are interested in

Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

• Marc Enßle,
• Stefan Buck,
• Roland Werz and
• Gerhard Maas

Beilstein J. Org. Chem. 2012, 8, 433–440, doi:10.3762/bjoc.8.49

• ][6][7][8] illustrate the wide range of applications. As far as sulfonium ylides are concerned, thermally induced isomerisation, that is the 1,2-shift of a substituent (Stevens rearrangement) and [2,3]-sigmatropic rearrangement of allylsulfonium ylides [9][10][11], and the use as C1 building blocks in

• -β-ketoesters 1, stable four- to seven-membered cyclic ylides 2 were obtained (Scheme 1); in the case of R2 = allyl, however, the ylides underwent a spontaneous [2,3]-sigmatropic rearrangement. On the other hand, the conversion of methionine-derived diazoketone 3 into the cyclic sulfonium ylide 4 was

• simultaneous formation of five-ring sulfonium ylide 12c and six-ring carbonyl ylide 14c is immediately followed by intramolecular pericyclic reactions with participation of the allylic π-system. Sulfonium ylide 12c rearranges by the expected [2,3]-sigmatropic rearrangement [3][10][16] to form