ABSTRACT
Nearly a century after their original discovery, catalyzed enantioselective variants of the venerable Claisen rearrangement remain relatively rare. We have discovered a cooperative transition metal-Lewis acid cocatalyst system that affects highly enantio- and diastereoselective examples of archetypical Claisen rearrangements. The catalyzed rearrangements proceed using an easily prepared enantioenriched transition metal catalyst and a commercially available Lewis acid cocatalyst at ambient temperature in common solvents.
Subject(s)
Aldehydes/chemical synthesis , Vinyl Compounds/chemistry , Aldehydes/chemistry , Catalysis , Molecular Structure , Organometallic Compounds/chemistry , Ruthenium/chemistry , StereoisomerismABSTRACT
A ring-closing metathesis-based strategy has allowed access to an unreported pair of pyridoisoindolones and their previously unknown sultam counterparts. The synthetic routing takes advantage of the ready availability of N-allylphthalimide and N-allylsaccharin and proceeds via the proper incorporation of small side chains into the heterocyclic ring. Positionally selective introduction of the conjugated diene functionality was realized efficiently. Detailed study of the excited-state chemistry of 7 and 8 showed both lactams to be subject to [4 + 2] dimerization under acetone-sensitized conditions. Different regioselectivities are involved, with the response of 8 being far more efficient than that exhibited by 7. No dimers could be isolated from the photolyzates of 9 and 10 under any conditions. While the latter sultam undergoes extensive polymerization, 9 is transformed via direct irradiation at 350 nm into 46 and 47 via [1,3]-sigmatropy involving the S-N bond and heterocyclic ring cleavage, respectively.
Subject(s)
Isoindoles/chemistry , Pyridines/chemistry , Sulfanilamides/chemistry , Cyclization , Isoindoles/chemical synthesis , Molecular Structure , Photochemistry , Pyridines/chemical synthesis , StereoisomerismABSTRACT
The title compound, C(12)H(12)BrNO(2)S, was isolated after direct irradiation (hν 350â nm, hexa-ne) of a mixture of stereoisomeric sulfonamides containing a vicinal dibromide and a conjugated diene. This product is one of a group of substrates that has contributed to our understanding of the photoreactivity patterns of non-bridged sulfonamides. The crystal structure was determined from a non-merohedrally twinned data set, where the twin law corresponded to a 180° rotation about the a* axis. The minor twin component refined to a value of 0.176â (3). The conformation of the mol-ecule is planar at one end, as the benzene ring and the adjacent fused five-membered ring are coplanar, and U-shaped at the other end, where the five-membered ring is fused to the heterocyclic six-membered ring containing an allyl bromide group.
ABSTRACT
The title compound, C(15)H(22)O(3), was prepared via amino-acid-promoted Robinson annulation followed by tandem Pd/C-mediated hydrogenation and oxidative cyclization. This product was instrumental in determining the feasibility of a stereocontrolled hydrogenation in which the directing hydroxyl group is adjacent to the 6-7-ring network and its olefinic component. The asymmetric unit consists of a single mol-ecule with normal geometric parameters. The absolute configuration was assigned based on the known enanti-omeric prescursor. Inter-molecular C-Hâ¯O inter-actions link each mol-ecule with four neighboring mol-ecules.
ABSTRACT
A convergent strategy has allowed access to bridgehead sultam 9 and the related carboxamides 10 and 11. The synthetic routing proceeds via the coupling of a suitably constructed dienamine to either o-iodobenzenesulfonyl chloride or o-iodobenzoyl chloride to generate the amides. The application in sequence of ring-closing metathesis and an intramolecular Heck reaction gave rise to advanced tricyclic intermediates. The final two steps involved bromination in liquid bromine and proper 2-fold dehydrobromination. The latter maneuver was best achieved with tetrabutylammonium fluoride in DMSO at elevated temperature. While the irradiation of 9 led principally via SO2-N bond homolysis and [1,5] sigmatropic rearrangement to generate 37, 10 proceeded via disrotatory cyclization to the exo cyclobutene 39, and 11 resisted photoisomerization. The inertness of 11 may stem from its distorted structural features which force its conjugated diene double bonds to be rigidly oriented 32 degrees out-of-plane. The unique ability of the sulfonamide linkage to excited-state homolysis holds comparative interest.
ABSTRACT
Triplet-sensitized irradiation of 8-thia-9-azatricyclo[7.2.1.0(2,7)]dodeca-2,4,6,10-tetraene (16) in acetone solution gives rise exclusively to tetracyclic sultam 20. This strong preference for benzo-vinyl bridging distal to the sulfonamide functional group has also been observed in eight derivatives carrying chemically diverse functional groups at C-10. In none of these examples is regiospecificity eroded. This overall result suggests that the added substituents act in harmony with the electronic rebonding pathway found operative in the parent system. From the structural perspective, this transformation constitutes a facile means for accomplishing the ring contraction of a bridgehead sultam.