Photochemistry of phenoxybenzyl alcohols in aqueous solution: photosolvolysis vs. photorearrangement to 6H-dibenzo[b,d]pyrans
作者:C. G. Huang、Peter Wan
DOI:10.1021/jo00016a009
日期:1991.8
The photochemistry of three phenoxybenzyl alcohols (1-3) has been studied in MeOH, CH3CN, and in aqueous solution. It was found that both of the ortho-substituted phenoxybenzyl alcohols 1 and 2 gave the corresponding 6H-dibenzo[b,d]pyrans 6 and 10, via a mechanism believed to involve initial aryl C-O bond homolysis followed by rearrangement to give a 2-(2'-hydroxyphenyl)benzyl alcohol (biphenyl) derivative, which subsequently undergoes a photocyclization reaction to the corresponding 6H-dibenzo[b,d]pyran. The quantum yield for formation of 6 (from 1) was 0.0073 in neutral 6:4 H2O-CH3CN. Lower quantum yields for formation of 6 were observed on photolysis in pure organic solvents (PHI = 0.0015 in 100% CH3CN). The meta-substituted isomer 3 did not give any reaction via a similar photocyclization process: its photochemistry involves initial aryl C-O bond homolysis followed by simple radical recoupling to give isomeric hydroxybiphenyls, as well as products derived from radical escape. In aqueous sulfuric acid solution (pH < 2), a competing acid-catalyzed photosolvolysis reaction was observed for all of these compounds (i.e., C-OH bond heterolysis with assistance of hydronium ion); it was the only observed reaction in moderately concentrated sulfuric acid solution.
Dichotomy of Atom-Economical Hydrogen-Free Reductive Amidation vs Exhaustive Reductive Amination
作者:Pavel N. Kolesnikov、Dmitry L. Usanov、Karim M. Muratov、Denis Chusov
DOI:10.1021/acs.orglett.7b02821
日期:2017.10.20
Rh-catalyzed one-step reductive amidation of aldehydes has been developed. The protocol does not require an external hydrogen source and employs carbon monoxide as a deoxygenative agent. The direction of the reaction can be altered simply by changing the solvent: reaction in THF leads to amides, whereas methanol favors formation of tertiaryamines.