We report the total synthesis of (±)-aspidophylline A, one of many complex furoindoline-containing alkaloids that has not been synthesized previously. Our route features a number of key transformations, including a Heck cyclization to assemble the [3.3.1]-bicyclic scaffold as well as a late-stage interrupted Fischer indolization to install the furoindoline and construct the natural product's pentacyclic framework.
Zeolite A (LTA) has many large-scale
uses in separations and ion
exchange applications. Because of the high aluminum content and lack
of high-temperature stability, applications in catalysis, while highly
desired, have been extremely limited. Herein, we report a robust method
to prepare pure-silica, aluminosilicate (product Si/Al = 12–42),
and titanosilicate LTA in fluoride media using a simple, imidazolium-based
organic structure-directing agent. The aluminosilicate material is
an active catalyst for the methanol-to-olefins reaction with higher
product selectivities to butenes as well as C5 and C6 products than the commercialized silicoalumniophosphate or
zeolite analogue that both have the chabazite framework (SAPO-34 and
SSZ-13, respectively). The crystal structures of the as-made and calcined
pure-silica materials were solved using single-crystal X-ray diffraction,
providing information about the occluded organics and fluoride as
well as structural information.
The akuammiline alkaloids are a family of intricate natural products which have received considerable attention from scientists worldwide. Despite the fact that many members of this alkaloid class were discovered over 50 years ago, synthetic chemistry has been unable to address their architectures until recently. This minireview provides a brief overview of the rich history of the akuammiline alkaloids, including their isolation, structural features, biological activity, and proposed biosyntheses. Furthermore, several recently completed total syntheses are discussed in detail. These examples not only serve to highlight modern achievements in alkaloid total synthesis, but also demonstrate how the molecular scaffolds of the akuammilines have provided inspiration for the discovery and implementation of innovative cascade reactions for the rapid assembly of complex structures.
A series of monoquaternary and diquarternary benzyl-imidazolium derivatives are prepared and used as organic structure direction agents (OSDAs) in germanosilicate syntheses. The goal of this work is to create new multidimensional large pore zeolites. For the OSDA made and tested, we looked for relationships based upon stereochemistry from the benzyl ring as part of each structure. Several known molecular sieves with the *BEA, BEC, IWS, or LTA topologies are obtained. Molecular modeling is carried out with the goal of understanding: (a) the product selectivity correlation with the OSDA and the zeolite obtained, and (b) why differential rates of crystallization are observed for isomers that lead to different zeolite products. Additionally, a new molecular sieve denoted CIT-13 is prepared and shown to possess intersecting 14-and 10-membered ring pores, which gives confidence to the soundness of this approach for OSDA construction to yield new multidimensional large pore zeolites. CIT-13 is the first molecular sieve to have this combination of pore sizes.
We report the first total synthesis
of the complex akuammiline
alkaloid picrinine, which was first isolated nearly five decades ago.
Our synthetic approach features a concise assembly of the [3.3.1]-azabicyclic
core, a key Fischer indolization reaction to forge the natural product’s
carbon framework, and a series of delicate late-stage transformations
to complete the synthesis. Our synthesis of picrinine also constitutes
a formal synthesis of the related polycyclic alkaloid strictamine.
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