Engineering Reactions in Crystalline Solids:  Photochemical Generation of Secondary and Tertiary Enol Radical Pairs from Crystalline Ketodiesters

Abstract

The photochemical decarbonylation of several crystalline 1,3-acetonedicarboxylates has been analyzed in solution and in the solid state. It is shown that the efficiency of the solid-state reaction depends on the stability of the intermediate acyl-alkyl and alkyl-alkyl radical pairs. Reactions proceeding through tertiary enol radicals are more efficient than reactions proceeding through secondary enol radical centers. Solid-state reactions that require the intermediacy of primary enol radicals do not occur. It is also shown that the selectivity of product formation in crystals depends on the structure of the reactant solid phase.

In the Twilight Zone between [2]Pseudorotaxanes and [2]Rotaxanes

“…Perchlorates were purchased from Aldrich. All the obtained esters were characterized by 1 H and 13 C NMR spectroscopy and the data were compared to those of authentic compounds, both commercially available ( 1b , 3b , 4b , 6b , 8b , 9b , 13b , 15b , 16b , 17b , 20b , 24b , 1c , 2c , 17c ) or previously reported ( 2b ,23 5b ,24 7b ,24 10b ,25 14b ,26 18b ,27 19b ,28 22b ,29 1d ,30 1e ,31 1f ,31 1g ,31 5c 32). 1 H NMR experiments were recorded at 300 MHz with a Varian Gemini instrument.…”

Taming Radical Pairs in Nanocrystalline Ketones: Photochemical Synthesis of Compounds with Vicinal Stereogenic All-Carbon Quaternary Centers

“…In order to develop a general and predictive model for the photodecarbonylation reaction, one can take acetone as a standard and look at the effects of α,α′-substitutents on the intermediates along the reaction coordinate (Scheme ). , The values indicated in parentheses include the heats of formation for acetone (−51.9 kcal/mol), acetyl and methyl radicals (32.6 kcal/mol), and CO plus two methyl radicals (43.6 kcal/mol) at ambient conditions. The singlet and triplet excitation energies of acetone were added to the ground-state value to estimate the heats of formation of the singlet (36.1 kcal/mol) and triplet (28.1 kcal/mol) excited states.…”

“…One of the earlier tests of the relationship between radical stabilization and solid-state photoreactivity included a series of acetone diadamantyl esters, 11a – e (Scheme ). These compounds were all crystalline, and by increasing the number of methyl groups on the two α-positions we were able to change the RSE values from −8.9 kcal/mol for 11a to −19.79 kcal/mol for 11e . In order to compare the effect of radical stabilizing substituents, each of these ketones were irradiated in dilute benzene solutions and as fine crystalline powder.…”

“…Photodecarbonylation reaction of ketones 11a – e as a function time in the solid state. Reproduced with permission from ref . Copyright 2001 American Chemical Society.…”

11 Organic photochemistry

“…Solid-state irradiation of diadamantyl-1,3-acetonedicarboxylates 153 results in decarbonylation, with the chemical efficiency correlating with the stability of the intermediate radicals governed by the α-methyl substituents (Scheme 70). 95 The reaction in crystal proceeds with geminate radical recombination, whereas the solution phase reaction includes random radical-radical combinations.…”