Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• vinylogous amides such as 11, however, we fortuitously found substituted 2,3-dihydro-1H-pyrrolizines 12 as unexpected products when intermediates 11 were exposed to acidic conditions, including treatment with acetic acid or even during chromatography on silica gel (Scheme 1) [18]. In these cyclizations the

• N-phenacyl analogue 11 (Ar = Ar’ = Ph), the ester-containing enaminone 15a proved to be completely stable during chromatography on silica gel or upon dissolution in acetic acid at room temperature (conditions under which we had observed cyclization of vinylogous amides 11 [18]), and spontaneous

• acid efficiently yielded ethyl 6,7-diphenyl-2,3-dihydro-1H-pyrrolizine-5-carboxylate (29) (82%). Conclusion A variety of N-(ethoxycarbonylmethyl) vinylogous amides prepared in three steps from pyrrolidin-2-one (16) or piperidin-2-one (23) underwent cyclization to yield 2,3-dihydro-1H-pyrrolizines 19 or

Regiodivergent condensation of 5-alkoxycarbonyl-1H-pyrrol-2,3-diones with cyclic ketazinones en route to spirocyclic scaffolds

• Alexey Yu. Dubovtsev,
• Maksim V. Dmitriev,
• Аndrey N. Maslivets and
• Michael Rubin

Beilstein J. Org. Chem. 2017, 13, 2179–2185, doi:10.3762/bjoc.13.218

• . Indeed, these highly electrophilic cyclic vinylogous amides are known to undergo facile nucleophilic additions [21][22][23][24][25], sometimes accompanied with subsequent pericyclic rearrangements [26][27][28][29][30][31][32][33]. Not surprisingly, these versatile synthons have been successfully employed

An intramolecular C–N cross-coupling of β-enaminones: a simple and efficient way to precursors of some alkaloids of Galipea officinalis

• Hana Doušová,
• Radim Horák,
• Zdeňka Růžičková and
• Petr Šimůnek

Beilstein J. Org. Chem. 2015, 11, 884–892, doi:10.3762/bjoc.11.99

• be considered vinylogous amides. Hence, their nucleophilicity is lowered and enaminones can be more challenging substrates for C–N cross-coupling compared to ordinary enamines. We used 3a as the model substrate for the optimization study. The reaction conditions were surveyed from the following

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

Establishing the concept of aza-[3 + 3] annulations using enones as a key expansion of this unified strategy in alkaloid synthesis

• Aleksey I. Gerasyuto,
• Zhi-Xiong Ma,
• Grant S. Buchanan and
• Richard P. Hsung

Beilstein J. Org. Chem. 2013, 9, 1170–1178, doi:10.3762/bjoc.9.131

• synthesis; catalysis; enones; intramolecular aza-[3 + 3] annulation; N-heterocycles; natural product; vinylogous amides; Introduction Throughout the past decade, we have been developing an aza-[3 + 3] annulation reaction as a general and unified strategy in alkaloid synthesis [1][2][3][4][5][6][7][8][9][10

• handled vinylogous amides and vinyl iminium salts. It provides a significant complementary, if not superior, approach to aza-[4 + 2] cycloadditions in constructing piperidines, because the aza-dienes and imines required are not always the most accessible and/or easily handled substrates given the problems

• ][13][14][15]. The intramolecular variant of this annulation has proven to be particularly valuable for total synthesis [16][26][27][28][29][30][31][32]. Specifically, the intramolecular aza-[3 + 3] annulation of vinylogous amides tethered to a vinyl iminium motif 1a proceeds through a tandem sequence

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• synthesis of Vitamin B12 by the groups of Woodward and Eschenmoser [130], this synthesis utilized a powerful methodology developed during this period to make vinylogous amides [131][132]. Pyrrolidinethione 176 was reacted with the dibromoester 177 to give the Z isomer of the vinylogous carbamate 178 (Scheme