Diols catalytic dehydrogenation

Synthesis from Citronellol. Citronellol is hydrated to 3,7-dimethyloctan-l,7-diol, for example, by reaction with 60% sulfuric acid. The diol is dehydrogenated catalytically in the vapor phase at low pressure to highly pure hydroxydihydrocitronellal in excellent yield. The process is carried out in the presence of, for example, a copper-zinc catalyst [68] at atmospheric pressure noble metal catalysts can also be used [69]. 

Because the conversion of primary diols into lactones is accomplished not only by oxidizing agents but also by catalytic dehydrogenation, it is likely that the reaction takes place stepwise via hemiacetal intermediates (equation 294) [355]. 

Zeng H, Guan Z (2011) Direct synthesis of polyamides via catalytic dehydrogenation of diols and diamines. J Am Chem Soc 133 1159... 

Compound 85 was dehydrogenated at 300° over palladium black under reduced pressure to a pyridine derivative 96 which was independently synthesized by the following route. Anisaldehyde (86) was treated with iodine monochloride in acetic acid to give the 3-iodo derivative 87. The Ullmann reaction of 87 in the presence of copper bronze afforded biphenyldialdehyde (88). The Knoevenagel condensation with malonic acid yielded the unsaturated diacid 91. The methyl ester (92) was also prepared alternatively by a condensation of 3-iodoanisaldehyde with malonic acid to give the iodo-cinnamic acid (89), followed by the Ullmann reaction of its methyl ester (90). The cinnamic diester was catalytically hydrogenated and reduced with lithium aluminium hydride to the diol 94. Reaction with phosphoryl chloride afforded an amorphous dichloro derivative (95) which was condensed with 2,6-lutidine in liquid ammonia in the presence of potassium amide to yield pyridine the derivative 96 in 27% yield (53). 

Second, 1,4-diols undergo intermolecular hydrogen transfer, giving lactones efficiently in acetone containing Cp Ru(P-N) catalysts the TOF of this reaction at 30 C exceeds 1,000 h (Fig. 21) [67]. The catalytic oxidative lactonization of diols is characterized by its unique chemo- and regioselectivity. The significant rate difference between primary and secondary alcohols in dehydrogenation, and the rate difference between 1,4-diols and 1,5- or 1,6-diols enable unique oxidative lactonization of triols. 

Ishii and coworkers reported that the JV-heterocyclization of naphthylamines with diols can be achieved with an iridium catalyst. In a typical example, the reaction of 1-naphthylamine with 1,3-propanediol was carried out with a catalytic amount of IrClg (5 mol%), r c-2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) (10 mol%), and the corresponding 7,8-benzoquinoline was obtained in 96% yield (Scheme 11.11) [159]. The proposed reaction mechanism indicates that the imine intermediate is formed by the reaction of the amine and aldehyde by Ir-catalyzed dehydrogenation. Subsequent hydrogenation by the in situ generated Ir hydride leads to an aminoalcohol followed by cyclization to the desired quinoline products. 

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