A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• radical adds to the central carbon of the allene giving a conjugated N-acyliminium that undergoes nucleophilic addition by arylamines and alcohols. Keywords: allenamide; allene; intermolecular; N-acyliminium; photoredox; Introduction Allenamides (Scheme 1, 1) and their congeners have attracted

• considerable attention over the past 15 years due to their characteristic reactivity profiles [1][2][3][4]. The reactivity that an allenamide can display is distinct from a traditional allene due to the presence of an amide unit attached at the α-carbon. This substituent can donate electron density into the

• allene, principally onto the central β-carbon, that can be harnessed in subsequent chemical transformations leading to regiochemical confidence in the resulting products (Scheme 1). Importantly, this unique reactivity has underpinned allenamide chemistry and led to the development of a number of

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• (results are collected in Table 2). Desilylation of alkynes 6k and 6j under alkaline conditions with K2CO3, in analogy to the description of Vasella et al. [57] leads to instant decomposition of the starting material in a base-promoted propargyl–allenamide isomerization. According to our hypothesis, basic

A strategic approach to [6,6]-bicyclic lactones: application towards the CD fragment of DHβE

• Tue Heesgaard Jepsen,
• Emil Glibstrup,
• François Crestey,
• Anders A. Jensen and
• Jesper Langgaard Kristensen

Beilstein J. Org. Chem. 2017, 13, 988–994, doi:10.3762/bjoc.13.98

• allenamide 14 as the major product [21]. After extensive optimization, the optimal results were obtained by treatment of 13 with 1 equiv of LiHMDS at −78 °C for 2 h before the addition of 5 equiv of ethyl chloroformate. The resulting mixture was then left at –78 °C for 1 h before quenching at low temperature

• , which proved vital to avoid the allenamide formation. The careful control of the reaction conditions in this way provided the desired product 15 in 73% yield and the subsequent Z-stereoselective addition of LiI proceeded without problems to give (Z)-16 in 89% yield. Unfortunately, performing the

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

• Armando Navarro-Vázquez

Beilstein J. Org. Chem. 2015, 11, 1441–1446, doi:10.3762/bjoc.11.156

• predict the experimentally observed behavior for several examples from the literature. Keywords: allenamide; DFT; isomerization; ynamide; Introduction Allenamides [1][2] and ynamides [3][4][5] have become useful functional groups for organic chemistry synthesis in the last years. Reduced electron pair

• propargyl bromide (Scheme 1) [6][7]. Subsequent base-catalyzed isomerization of N-propargyl compound 2 leads to allenamide 3. Whereas in some particular cases the reaction leads to the final N-alkynyl product, in most cases, the reaction stops at the allene stage and does not further progress even when

• due to thermodynamic rather than kinetic reasons, and it is not necessarily the case that ynamides are more stable than the parent allenamides. Here it is hypothesized that N-propargylamide ↔ allenamide ↔ ynamide interconversion takes place reversibly and the outcome of the reaction is related to the

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• ], allowing the construction of six-membered adducts with up to three new stereogenic centers with complete diastereoselectivity and enantioselectivities of up to 91% ee (R1, R2 = Me, R4 = Ph, Scheme 11). With regard to the mechanism, it has been proposed that the activation of the allenamide by the gold

• investigations by the groups of Mascareñas, González and Chen revealed that the gold-catalyzed cycloaddition between an allenamide and an appropriate alkene (e.g., enamide, enol ether or vinylarene) provides a variety of cyclobutanic systems in excellent yields. The optimum catalysts for the racemic processes

• methods that affords optically active cyclooctanes by means of a catalytic enantioselective process. Also recently, Chen and co-workers demonstrated that gold-activated allenamide species can participate in [3 + 2] cycloadditions with azomethine imines or nitrones under catalysis with Ph3PAuCl/AgOTf or

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

• Benito Alcaide,
• Pedro Almendros,
• M. Teresa Quirós and
• Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

• one heteroatom are rare [43][44][45][46][47][48]. Besides, it has been reported very recently that the Au(I)-catalyzed cyclization of a N-phenethyl-N-Boc-protected allenamide failed [49]. Despite the above precedents, but in continuation of our interest in heterocyclic and allene chemistry [50][51][52

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• quadruple-cascade reaction exemplifies an efficient three-component reaction. In 2010 Wang et al. [11] reported the highly enantioselective synthesis of trisubstituted chiral 4H-chromenes 20 through iminium-allenamide catalysis. The reaction consists of a Michael–Michael-cascade sequence between alkynals 5

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• and mild synthesis of enamides (193–196) by a gold-catalyzed nucleophilic addition to allenamides 191 (Scheme 36) [87]. For example, treatment of allenamide and 1-methylindole with 5.0 mol % of PPh3AuNTf2 in CH2Cl2 at room temperature gave the corresponding enamide in 83% yield. Gold-catalyzed direct

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• ; however, our justification is that since there are few well established routes for preparing amido-dienes, our allenamide isomerization strategy (for reviews on allenamide chemistry see [21][22][23], for reports in 2009, 2010 and 2011 see [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40

• ][57][58]) suffer from limited access as well as the instability of halo-dienes (Scheme 2). In contrast, multi-substituted allenamides can be concisely prepared through α-alkylations of a parent allenamide [47][59] (for the synthesis of parent allenamides see [60]) or amidative cross-couplings of

• allenyl halides [61][62]. Therefore, our allenamide isomerization strategy has a much greater synthetic potential in constructing amido-dienes. While the chemistry of 1-amido-dienes has been explored in some detail (see Scheme 3 for success in preparing 1-amido-dienes via allenamide isomerizations) [63