Strong and Confined Acids Control Five Stereogenic Centers in Catalytic Asymmetric Diels–Alder Reactions of Cyclohexadienones with Cyclopentadiene

Abstract

We describe a highly enantioselective Diels–Alder reaction of cross‐conjugated cyclohexadienones with cyclopentadiene, in which five stereocenters are effectively controlled by a strongly acidic and confined imidodiphosphorimidate catalyst. Our approach provides tricyclic products in excellent stereoselectivity. We also report methods to convert the obtained products into useful intermediates and a computational study that aids in gaining deeper insight into the reaction mechanism and origin of stereoselectivity.

Unusual In‐Situ Preorganization and Postoxidation Steps Observed in Diels‐Alder Reactions of Styrylcyclohexene Dienes

“…Literature survey shows that there are instances, where unusual products are obtained during some of the DA reactions. These phenomena are usually due to either initial rearrangement of the diene/dienophile [16] before the cycloaddition step, unexpected formation of dienes from other substrates, [17] unanticipated additional spontaneous rearrangement, [18] isomerization [19] or functionalization [20] of the DA adducts, and creation of a fifth stereogenic center in the product [21] . Among these many unusual observations, however, we could spot only two DA reactions in which the final products have ended up with an additional hydroxyl functionalization.…”

(R)‐BINOL‐6,6’‐bistriflone: Shortened Synthesis, Characterization, and Enantioselective Catalytic Applications

“…Toward this end, the crucial influence of an electron‐withdrawing substituent, namely a NO 2 group, in the 6,6′‐positions of the BINOL scaffold was also demonstrated [11] . More generally, the introduction of a triflyl group proved determining for increasing catalytic activity [12–13] …”

The Silicon–Hydrogen Exchange Reaction: Catalytic Kinetic Resolution of 2-Substituted Cyclic Ketones

“…[5][6][7] Our studies commenced with the identification of a proper acid catalyst for the asymmetric silicon-hydrogen exchange reaction of 2-phenylcyclohexan-1-one (1a) and methallylsilane 2. 8 As Hui Zhou a Pinglu Zhang a, b Benjamin List* a Synlett Letter / Cluster / New Tools Template for SYNLETT Thieme reported in our previous work, while moderately acidic Brønsted acids, such as chiral phosphoric acids (CPA) 9 imidodiphosphates (IDP), 10 and disulfonimides (DSI) 11 were ineffective, the desired enol silane products were obtained under the catalysis of the much more acidic IDPi catalysts (see the supporting information, table S1). 12,13 The thermodynamically favoured enol silane 4a was observed to be the major product (3a:4a = 1:2) when the reaction was performed at 25 °C in toluene-d8 using IDPi 5a, and replacement of the Tf substituent with a C6F5SO2 group gave catalyst 5b, which led to an even higher 3a:4a ratio of 1:5.…”

“…Note: ((perfluoronaphthalen-2-yl)sulfonyl)phosphorimidoyl trichloride R6 and the 3,3'-disubstituted BINOL8 were previously reported. (S,S)-IDPi 5e:…”