Total Synthesis of Ulodione A via a Double-Alkylation and DABCO Promoted Ring-Expansion Rearrangement Sequence.

First total synthesis of ulodione A has been achieved via the key-step reactions of DIPEA-promoted dialkytion of 1,3-cyclopentadione with a bromonitroolefin and DABCO promoted/catalytic semipinacol-like ring-expansion rearrangement, with regioselective transformation of the nitrocyclohexane intermediates to their cyclopentenone counterparts via a sequence of reactions in a one-pot operation. Structures of six products were unequivocally established by X-ray crystallography.

Control of the Organocatalytic Enantioselective α-Alkylation of Vinylogous Carbonyl Enolates for the Synthesis of Tetrahydropyran Derivatives and Beyond.

The organocatalytic α-alkylation of vinylogous carbonyl compounds to hydroxynitroolefins for the synthesis of hemiacetals was realized with excellent enantioselectivities and in high yields. High diastereoselectivity (up to >20:1) has been accomplished with the addition of Et3N. The α- and γ-alkylation of vinylogous ketone against nitroolefins displayed high but opposite facial selectivities. Transformation of the hemiacetal products to other polycyclic compounds, including the euroticin B analog, has been demonstrated.

Analytical tests to evaluate pozzolanic reaction in lime stabilized soils.

Shrink-swell soils are predominant in various parts of the parts of the world. Lime has been extensively used to reduce the shrink-swell mechanism as it chemically reacts with soil minerals forming pozzolanic products such as calcite and calcium-silicate-hydrate (C-S-H). Conventionally, whether chemical treatment of soils results in effective pozzolanic stabilization reactions is determined anecdotally through engineering tests including unconfined compressive strength, plasticity index (PI), and pH tests. This study builds on existing literature regarding how more direct quantification of pozzolanic products can be obtained through tests that directly identify and quantify pozzolanic products, specifically in lime-treated clay soils. Specifically, x-ray diffraction (XRD) and differential thermogravimetric analysis (DTA) are used for this testing. Expansive soils with plasticity indices above 25% were selected for this study. Engineering tests on these lime-treated soils indicated significant improvement in strength and reduction in PI. In XRD analysis, pozzolanic products are assessed by the location and intensity of x-ray peak(s). The XRD data show a decrease in the intensity of alumio-silicate minerals such as kaolinite and smectite; silica and alumina are dissolved at a high pH and converted to pozzolanic products such as calcium-silicate-hydrate (C-S-H). DTA indicates the presence of C-S-H with the characteristic weight loss from 140°C to 250°C.The methodology describes the following: ● Sample preparation steps for XRD and DTA analysis. ● Analysis of XRD results and DTA analysis.

Catalytic 1,2-Rearrangements: Organocatalyzed Michael/Semi-Pinacol-like Rearrangement Cascade of 1,3-Diones and Nitroolefins.

New types of organocatalytic 1,2-rearrangements, which resemble the Smiles-like or semi-pinacol-like rearrangement, of Michael adducts of 1,3-dicarbonyl-2-alkyl compounds and nitroalkenes have been realized. Unlike the well-known conjugate addition, the reaction affords the 1-phenyl-1-nitroalkanes via unprecedented rearrangement and cascade reactions. Structures of the appropriate products were unambiguously characterized by X-ray crystallography.

Direct Transformation of Nitroalkanes to Nitriles Enabled by Visible-Light Photoredox Catalysis and a Domino Reaction Process.

A mild and convenient process for direct transformation of nitroalkanes to the corresponding nitriles was developed using a visible-light photoredox catalysis strategy with household decorative blue LEDs and the additives of Et3N and DIPIBA (or DIPEA). Application of the process in secondary nitroalkanes bearing a ß-alcohol resulted in a domino process of the retro-Henry reaction and the subsequent acetalization, aldol, cyanohydrin, and ring-contraction reactions with stereoselectivities. The photocatalytic reaction was demonstrated by a continuous flow method.

Catalyst- and Substituent-Controlled Switching of Chemoselectivity for the Enantioselective Synthesis of Fully Substituted Cyclobutane Derivatives via 2 + 2 Annulation of Vinylogous Ketone Enolates and Nitroalkene.

The first regioselective, diastereoselective, and enantioselective organocatalyzed Michael-Michael cascade of vinylogous ketone enolates and nitroalkenes for the construction of fully substituted cyclobutanes is achieved by the deployment of the appropriate chiral squaramide catalyst and the pertinent substituent on the substrate. The domino reaction provided cyclobutanes with four contiguous stereocenters, including a quaternary center in good yields with diastereomeric ratio of >20:1 and with enantioselectivities of mostly up to 98% enantiomeric excess (ee). The structures and the absolute configurations of the adducts were confirmed by single-crystal X-ray crystallographic analyses of the appropriate products.

Visible-light-induced C(sp3)-H activation for a C-C bond forming reaction of 3,4-dihydroquinoxalin-2(1H)-one with nucleophiles using oxygen with a photoredox catalyst or under catalyst-free conditions.

A convenient photocatalyzed oxidative coupling reaction of 4-alkyl-3,4-dihydroquinoxalin-2(1H)-one and its derivatives with a variety of nucleophiles was developed with a ruthenium photoredox catalyst and oxygen under a household compact fluorescent light. With a slower reaction rate, the cross coupling transformation can be achieved in the absence of an external photocatalyst with a similar isolated yield. An application to the synthesis of natural product cephalandole A was also demonstrated.