The development of a direct and highly stereoselective synthesis of 2,3,5‐substituted tetrahydrofurans has been accomplished through a combination of batch‐ and microchip‐MS‐experiments. This sequential transformation comprises a Lewis acid‐mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ‐bonds and three stereogenic centers in a one‐pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip‐MS‐experiments include a vinylogous aldol reaction and a Prins‐type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi‐ and tricylic products by carbonyl–ene reactions, proceeding with excellent yields and diastereoselectivity.
The development of a direct and highly stereoselective synthesis of 2,3,5-substituted tetrahydrofurans has been accomplished through a combination of batch- and microchip-MS-experiments. This sequential transformation comprises a Lewis acid-mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ-bonds and three stereogenic centers in a one-pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip-MS-experiments include a vinylogous aldol reaction and a Prins-type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi- and tricylic products by carbonyl-ene reactions, proceeding with excellent yields and diastereoselectivity.
An
organocatalytic, highly enantioselective addition of cyclic
enamides to in-situ-generated 3-methide-3H-pyrroles
with subsequent cyclization and elimination has been developed. This
protocol represents a novel and straightforward route toward polycyclic
cyclopenta[b]pyrroles with high yields and excellent
enantioselectivity. Central to the success is the formation of a chiral,
hydrogen-bonded 3-methide-3H-pyrrole upon phosphoric-acid-catalyzed
dehydration of the starting 1H-pyrrol-3-yl carbinol
that reacts with the enamide in a stepwise cycloannulation process.
We describe herein an organocatalytic, diastereo-and enantioselective [6 + 2]-cycloaddition toward the synthesis of densely substituted 2,3-dihydro-1H-pyrrolizines bearing three contiguous stereogenic centers which are obtained with good yields, as single diastereomers, and with excellent enantioselectivity. A crucial feature of this one-step process leading to a prominent structural motif in many biologically active natural products is a BINOL-derived phosphoric acid catalyzed reaction of 1H-pyrrole-2-yl carbinols with 2-vinylindoles via the corresponding hydrogen-bonded chiral 2-methide-2H-pyrroles.
An organocatalytic, highly diastereo-and enantioselective [6 + 2]-cycloaddition of 3-methide-3H-pyrroles with 2vinylindoles has been developed. This BINOL phosphoric acid-catalyzed reaction utilizes pyrrole-3-carbinols as precursors for the in situ generation of 3-methide-3H-pyrroles to access densely substituted cyclopenta[b]pyrroles bearing three contiguous stereogenic centers as single diastereomers in good yields with excellent enantioselectivity.
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