Electron-Transfer-Induced Reductive Cleavage of Phthalans: Reactivity and Synthetic Applications

Gram-Scale Synthesis and Supramolecular Complex of Precursors of Clar's Hydrocarbon Triangulene

We present to date the most efficient gram-scale synthesis of triangulene-4,8-dione and 12-hydroxytriangulene-4,8-dione, the precursors of Clar’s hydrocarbon, in overall yields >50%. The direct dihydroprecursors of triangulene, obtained upon reduction of triangulene-4,8-dione, were stabilized in a supramolecular complex with a tetracationic cyclophane ExBox⁴⁺ and characterized by single-crystal X-ray crystallography. This result represents the first step in an endeavor to stabilize the fragile core of triangulene in an inclusion complex in solution and solid state.

Benzene construction via Pd-catalyzed cyclization of 2,7-alkadiynylic carbonates in the presence of alkynes

A palladium-catalyzed highly regio- and chemo-selective cyclization of 2,7-alkadiynylic carbonates with functionalized alkynes to construct 1,3-dihydroisobenzofuran and isoindoline derivatives under mild conditions has been developed. Functional groups such as alcohol, sulfonamide, and indoles could be well tolerated. After careful mechanistic studies, a mechanism involving oxidative addition and regioselectivity-defined double alkyne insertions has been proposed.

One-Pot Synthesis of Rotationally Restricted, Conjugatable, BODIPY Derivatives from Phthalides

O-Ethylation of phthalides with Meerwein's reagent followed by reaction of the ensuing salts with pyrrole, results in the formation of 5-alkoxy-5-phenyl dipyrromethane derivatives, which function as ready precursors of ortho-substituted 8-aryl BODIPY derivatives by reaction with borontrifluoride etherate, an overall process that can be carried out in a one-pot operation.

A tandem reaction of benzyne with functionalized benzylidenephthalan to afford phenanthro[10,1-bc]furan

A tandem reaction of benzyne with functionalized benzylidenephthalan for the synthesis of a variety of phenanthro[10,1-bc]furans has been achieved for the first time in moderate to good yields. The reaction mechanism involves a Diels–Alder reaction and an intermolecular nucleophilic addition reaction as the key steps.

Diastereoselective protonation of lactam enolates derived from (R)-phenylglycinol. A novel asymmetric route to 4-phenyl-1,2,3, 4-tetrahydroisoquinolines

Highly diastereoselective protonation of chiral lactam enolates of 4-substituted-1,4-dihydroisoquinolin-3-ones is reported. Protonation and alkylation processes of these lactam enolates derived from phenylglycinol occur with opposite diastereofacial selectivity. This diastereoselective protonation has been applied to the asymmetric synthesis of (4S)-N-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline 9 obtained in up to 97% ee.

Cytochrome P450cam substrate specificity: relationship between structure and catalytic oxidation of alkylbenzenes

The oxidation by cytochrome P450cam (CYP101) of ethylbenzene and a series of substrates derived from it by addition of one, two, three, or four carbon atoms has been examined. For each of the 18 substrates, the shift in spin state due to substrate binding, the extent of coupled turnover to give organic products and uncoupled turnover to give H2O2 and H2O, and the identities of the organic products have been determined. The same studies have been carried out with the T185L and T185F mutants of P450cam in which the active site volume is decreased. The results show that no detectable correlation exists between the observed spin state change and any other parameter studied. For substrates of equal size, coupled and uncoupled turnover vary widely but both are maximized when the phenyl ring bears one large alkyl substituent or a methyl ortho to the largest alkyl substituent. The presence of substituents in addition to these decreases activity. In the absence of other changes, coupled turnover is correlated with the size of the largest substituent, but no such correlation exists for uncoupled turnover. Decreasing the size of the active site cavity by a T185L mutation generally increases coupled turnover without altering the dependence on the alkyl group size. A T185F mutation causes too great an active site perturbation for structure-activity studies. Substrate oxidation occurs preferentially at 2 degrees or 3 degrees C-H bonds of the largest substituent or on the benzylic methyl ortho to it. Aromatic hydroxylation only competes with the oxidation of nonbenzylic 1 degree C-H bonds. The extent of coupled turnover is a function of substrate shape, substrate size, and cavity size, but still elusive parameters control the extent of uncoupled turnover.