SYNTHESIS AND THE POTENTIAL USE AS ATOMIC OXYGEN PRECUSORS

OF POLYCYCLO AROMATIC THIOPHENE S-OXIDES

Xiaotian ZhengSept 14th, 2015

Introduction: Photodeoxygenation

• DBTO deoxygenation

• Atomic oxygen, O(3P), in condensed phase– Similar reactivity with O(3P) in gas phase– Selective– Highly reactive

• Accepted mechanism– Unimolecular S-O bond scission at T2 state leading to DBT and O(3P)

• Vast potential in the utility of DBTO

Electronic configuration of O(3P)

Potential energy diagram for the excited states and deoxygenation of DBTO

J. Phys. Org. Chem. 2014, 27, 630–639

Energies of the electronic states of thiophene-S-oxide as a func- tion of S–O separation at four levels of theory.

Introduction

• Shortcomings of DBTO– Abs < ~345nm– High energy photons NOT optimal for use in/with

systems of interest– Common laser lines > DBTO absorbance

Introduction:• Solution: Increase the size of the π-electron system to allow

absorption and therefore deoxygenation at higher wavelengths• Potential problem: Increasing the π-electron system could

change the mechanism of deoxygenation, or even prevent it

Introduction:

• Previous study: – Oxidized benzene, yielding phenol and the parent thiophene.

(Biphenyl is used as internal standard)– Oxidized 2-methylbutane, yielding 2-methyl-2-butanol – Oxidized tetrabutylammonium chloride, hypochlorite ion was detected. – Oxidized para-substituted aryl sulfides, yielded the aryl corresponding

aryl sulfoxides

J. Org. Chem. 2001, 66, 4576-4579.

Fingerprint Analysis

• Oxidize a substrate, compare types and ratios of products to those obtained with DBTO• Example, previously reported with DBSeO (substrate = toluene)

J. Am. Chem. Soc., 2004, 126 (49), 16058–16065

Synthesized thiophene S-oxides with red-shift in absorption

Oxidative Cyclodehydrogenation

Synthesis of compound 5

UV-vis spectra of compound 1-4 and 6

Conformation change

• The rapid racemization can populate the molecules into vibrational states above the S0.

• The energy needed to promote the molecule into S1 state is reduced.

Toluene test result

• Different fingerprints• Two types of carbons:

• Benzylic (yielding benzaldehyde & benzyl alcohol)

• Aromatic (yielding cresols)• The oxidant shift from aromatic to benzylic with the

increase of the conjugated π system.

  % yield relative to sulfide formation of oxidized products from toluene 

Compound  benzaldehyde benzyl alcohol o-cresol m- and p- cresol

1 3±1 5±1 20±1 18±1

2 1.7±0.4 3.4±0.6 5.5±0.3 2.7±0.2

3 2.4±0.5 5.1±0.8 9.8±0.8 5.6±0.3

4 8.3±1.1 11.8±1.8 2.8±0.4 1.3±0.2

6 2.1±0.5 4±1 3.8±0.9 2.4±0.6

Benzene test Results

• Again, different fingerprints

• Biphenyl is observed as a minor byproduct

 % yield relative to sulfide formation of oxidized products from 

benzeneCompound  phenol  biphenyl

1 34±3 0.6±0.12 14.3±1.3 0.58±0.023 12.8±0.6 0.6±0.14 7.2±0.9 1.07±0.176 11.1±0.8 0.83±0.03

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• Triplet quencher cannot decrease the quantum yield of 1• Sensitizers can increase the quantum yield of 1

J. Photochem. Photobiol. A, 2008, 198, 45–51

Unanswered Questions• T1 deoxygenation of 2-6

-Triplet quencher should decrease the quantum yield and increase cresol ratio in toluene test-Triplet sensitizer should increase the quantum yield and decrease cresol ratio in toluene test

Unanswered Questions• Mechanism change

-T2 deoxygenation is unfavorable in 2-4 and 6-Energy difference between S1 and T2

Unanswered Questions

• The product of T1 deoxygenation– Oxygenation transfer or less reactive oxygen

intermediate?

Questions?

Introduction: Photochemistry of Sulfoxides

• Inversion

Introduction: Photochemistry of Sulfoxides • α-cleavage

Synthesis scheme of Benzo[b] naphtho[2, 1- d] thiophene S-oxide(2)

Synthesis scheme of Benzo[b] naphtho[1, 2- d] thiophene S-oxide(3)

Synthesis scheme of Dinaphtho[2, 1- b:1', 2'- d] thiophene S- oxide(4)

Synthesis scheme of Benzo[b] phenanthro[9, 10- d] thiophene S-oxide(6)