Empirical underidentification in estimating random utility models: The role of choice sets and standardizations

A standard approach to distinguishing people's risk preferences is to estimate a random utility model using a power utility function to characterize the preferences and a logit function to capture choice consistency. We demonstrate that with often-used choice situations, this model suffers from empirical underidentification, meaning that parameters cannot be estimated precisely. With simulations of estimation accuracy and Kullback-Leibler divergence measures we examined factors that potentially mitigate this problem. First, using a choice set that guarantees a switch in the utility order between two risky gambles in the range of plausible values leads to higher estimation accuracy than randomly created choice sets or the purpose-built choice sets common in the literature. Second, parameter estimates are regularly correlated, which contributes to empirical underidentification. Examining standardizations of the utility scale, we show that they mitigate this correlation and additionally improve the estimation accuracy for choice consistency. Yet, they can have detrimental effects on the estimation accuracy of risk preference. Finally, we also show how repeated versus distinct choice sets and an increase in observations affect estimation accuracy. Together, these results should help researchers make informed design choices to estimate parameters in the random utility model more precisely.

Catalyst-Controlled Stereoselective Barton-Kellogg Olefination

Overcrowded alkenes are expeditiously prepared by the versatile Barton-Kellogg olefination and have remarkable applications as functional molecules owing to their unique stereochemical features. The induced stereodynamics thereby enable the controlled motion of molecular switches and motors, while the high configurational stability prevents undesired isomeric scrambling. Bistricyclic aromatic enes are prototypical overcrowded alkenes with outstanding stereochemical properties, but their stereocontrolled preparation was thus far only feasible in stereospecific reactions and with chiral auxiliaries. Herein we report that direct catalyst control is achieved by a stereoselective Barton-Kellogg olefination with enantio- and diastereocontrol for various bistricyclic aromatic enes. Using Rh2 (S-PTAD)4 as catalyst, several diazo compounds were selectively coupled with a thioketone to give one of the four anti-folded overcrowded alkene stereoisomers upon reduction. Complete stereodivergence was reached by catalyst control in combination with distinct thiirane reductions to provide all four stereoisomers with e.r. values of up to 99:1. We envision that this strategy will enable the synthesis of topologically unique overcrowded alkenes for functional materials, catalysis, energy- and electron transfer, and bioactive compounds.

Direct Photoexcitation of Ethynylbenziodoxolones: An Alternative to Photocatalysis for Alkynylation Reactions*

Ethynylbenziodoxolones (EBXs) are commonly used as radical traps in photocatalytic alkynylations. Herein, we report that aryl-substituted EBX reagents can be directly activated by visible light irradiation. They act as both oxidants and radical traps, alleviating the need for a photocatalyst in several reported EBX-mediated processes, including decarboxylative and deboronative alkynylations, the oxyalkynylation of enamides and the C-H alkynylation of THF. Furthermore, the method could be applied to the synthesis of alkynylated quaternary centers from tertiary alcohols via stable oxalate salts and from tertiary amines via aryl imines. A photocatalytic process using 4CzIPN as an organic dye was also developed for the deoxyalkynylation of oxalates.

Photocatalytic Decarboxylative Coupling of Aliphatic N-hydroxyphthalimide Esters with Polyfluoroaryl Nucleophiles

Polyfluoroarenes are an important class of compounds in medical and material chemistry. The synthesis of alkylated polyfluoroarenes remains challenging. Here we describe a decarboxylative coupling reaction of N-hydroxyphthalimide esters of aliphatic carboxylic acids with polyfluoroaryl zinc reagents (Zn-ArF ) via synergetic photoredox and copper catalysis. This method readily converts primary and secondary alkyl carboxylic acids into the corresponding polyfluoroaryl compounds, which could have a wide range of F-content (2F-5F) and variable F-substitution patterns on the aryl groups. Broad scope and good functional group compatibility were achieved, including on substrates derived from natural products and pharmaceuticals. Mechanistic study revealed that a [Cu-(ArF )2 ] species could be responsible for the transfer of polyfluoroaryl groups to the alkyl radicals.

Chiral Distorted Hexa-peri-hexabenzocoronenes Bearing a Nonagon-Embedded Carbohelicene

A new family of chiral saddle-helix hybrid nanographenes is reported. The first hexa-peri-hexabenzocoronene (HBC) analogues bearing a nine-membered carbocycle are presented. Furthermore, for the first time, π-extended carbo[n]helicenes containing a nine-membered ring as part of the helical moiety have been synthesized. The combination of a [5]helicene moiety and a nonagon ring in a single chiral motif induces a tremendous distortion from planarity into the nanographenic structures compared to other saddle-helix hybrids such as heptagon- and octagon-containing π-extended carbo[5]helicenes. In fact, the interplanar angle of the two terminal rings reaches the largest angle (134.8°) of a carbohelicene reported to date, thus being by far the most twisted helicene yet prepared. Photophysical properties evaluation showed improved absorption dissymmetry factors (|gabs |=4.2×10-3 ) in the new family of nonagon-containing π-extended carbo[5]helicenes.