Phosphole-based phosphahelicenes whiche ntail unprecedented phosphinamide functions have been prepared. One of these diastereomericp hosphinamides displays an unusualp ropensitytointermolecular photochemical [2+ +2] cyclizationleading to ab is-phosphahelicene. The reaction affords the head-totail heterochiral diastereomer with total regio-and diastereoselectivity.T he reactionh as been observed not only in solution but also in the solid state, as as ingle-crystal-to-single-crystal process,u nder either X-ray or sunlight irradiation. The solidstate arrangement of the starting compound strongly prefigures the geometry of the final dimeric species and accounts for the particular ease by which this reaction takes place. The second diastereomer of the phosphinamide does not undergo dimerization under analogous photochemical conditions which can be attributed to an unfavourable arrangement in the solid state.The inter-and intramolecular [2+ +2] photocyclization reactions of olefins provide privileged methods for the synthesis of strained cyclobutaned erivatives, including natural product frameworks. [1] In their most general variants, these reactions combinet wo different substrates, but they are commonly applied also to dimerization processes. An umber of literature examplesd emonstrate that these photodimerization reactions can occure asily in the solid state, since [2+ +2] cyclizationsr equire am inimumm olecular movement when the reacting double bonds adopt ap arallel arrangementi nt he crystal. [2] When needed, template groups and supramolecular effects have been employed to suitably align the reactingd ouble bonds, both in solid-state and in liquid-phase reactions, as well as to control the regio-and stereoselectivity of these cyclization reactions. [3] Among others, dimerizations of heterocycles, such as benzothiophene oxides, [4] coumarins, [5] indoles [6] and phospholes, [7] have been reported. In the wake of theses tudies, we have noticed recently a[ 2 + +2] dimerizationp rocess involving phospha-helicene oxidesinw hich the helical sequence of aromatic rings is terminated by af used phosphole unit. [8] Ther eaction took place exclusively on phospholes with unsubstituted double bonds and afforded ah ead-to-head dimer as a1 :1 mixture of diastereomers. The lack of diastereoselectivity has restricted so far the synthetic usefulness of these reactions,w hile the dimerization itself hampered the synthesis of phosphahelicene oxides under photochemical conditions. In order to overcome this last limitation, substitution of the phosphole double bond by an aryl group has been leveraged in furtherstudies. [9] Herein we report the [2+ +2] photodimerization of an ew series of phosphahelicene derivatives, 5,w hich contain ap hosphinamide functionality.W ed emonstratet hat, in this series, phosphahelicenes may undergo diastereoselective head-to-tail [2+ +2] photocyclization reactions, and also show that the photoresponsive behaviour persists in the solids tate. The solidstate processh ighlightst he first single-crys...
This study discloses the first enantioselective variant of the gold(I)-catalyzed hydrative cyclizations of ynamides, which have been implemented by using bis-gold(I) complexes of chiral diphosphines. Starting from N-propargyl-ynamides and water in the presence of p-toluenesulfonic acid, the cyclization reactions afford N-tosyl-3,6-dihydropyridin-2(1H)-ones in good isolated yields and with high levels of stereocontrol (20 examples, enantiomeric ratios up to 94:6).
1,5‐Benzothiazepine frameworks are highly relevant in medicinal chemistry. Reported catalytic asymmetric approaches to these scaffolds have targeted 2,3‐dihydro‐1,5‐benzothiazepin‐4‐ones but leave the corresponding amines (i.e., 2,3,4,5‐tetrahydro‐1,5‐benzothiazepines) out of reach. Herein, we present the first entry to these important compounds in enantioenriched form. Our approach is based on the catalytic asymmetric sulfa‐Michael addition of 2‐aminothiophenols to trans‐chalcones, followed by intramolecular reductive amination. Both reactions required careful study to solve several challenging issues. The resulting optimized two‐step protocol afforded a range of 2,3,4,5‐tetrahydro‐1,5‐benzothiazepines as single trans diastereomers in moderate to good yields and enantioselectivities.
Phosphahelicenes with thiophosphinic acid and ester functionsh ave been obtained by the oxidative photocyclisation of olefins bearing both ab enzophenanthrene and ab enzophospholeu nit. When the methodh as been extended to olefins bearing ap artially saturated benzophospholeneu nit, ad ivergent regioselectivity of the photocycli-sations tep has been observed, leading to new helicenes in whicht he phosphorus function is located on the external rim of the helical backbone.T he observed regioselectivity correlates well with the free-valence numbers of the atoms involvedi nt he photocyclisation reaction(DFT calculations).
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