658699-37-7Relevant articles and documents
Chasing Polycyclic Natural Products: 5/6/5- or 5/6/6-Carbotricyclic Scaffold Construction via Stereodivergent Diels-Alder Reaction of Chiral Hydrindanes and Their Boron Complexes
Bauer, Florian,Claasen, Birgit,Fellmeth, Thomas,Frey, Wolfgang,K?hn, Andreas,Laschat, Sabine,St?ckl, Yannick,Wank, Bianca,Zens, Anna
supporting information, (2022/02/25)
Chiral trans-hydrindanes (bicyclo[4.3.0]nonanes) are important building blocks of polycyclic natural products. In order to access 5/6/5- and 5/6/6-carbotricyclic scaffolds scope and limitation of [4+2] cycloadditions of tetrahydroindanones with various dienes were studied. Cyclopentadiene gave a tetracylic endo-(R,R)-diastereomer under acid-catalysis, whereas thermal conditions provided the endo-(S,S)-diastereomer with the opposite diastereofacial selectivity. The stereodivergent outcome was rationalized by high-level quantum-chemical computations which revealed the acid-catalysis to be a kinetically controlled reaction and the thermal cycloaddition to be under thermodynamic control. Stereochemical assignment of the cycloadducts was facilitated by conversion of the 1,3-dicarbonyls with BF3 ? OEt2 into BF2-chelate complexes. Subsequent thermal Diels-Alder reaction of BF2- or BBN-chelates (from 9-BBN-OTf) gave endo/exo-mixtures of the (R,R)- and (S,S)-diastereomers, while more elevated temperatures yielded primarily the endo/exo-(S,S)-diastereomers. Thermal [4+2] cycloadditions with 2,3-dimethylbutadiene proceeded with lower diastereoselectivity as the reaction was kinetically controlled according to calculations. Attempted Diels-Alder-reactions with furan gave furyl-substituted indanones rather than cycloadducts.