1.5- Dioxygenated compounds

Analysis First convert the 1,6-dioxygenated compound to a 1,6-dicarbonyl compound, keeping the two carbonyl groups different ... 

The ozonolysis of cyclohexene to 1,6-dioxygenated compounds is shown in Figure 17.28. Other cycloalkenes similarly afford other l,y-dioxygenated cleavage products. With the three methods for workup (Figure 17.27), this ozonolysis provides access to 1,6-hexanediol, 1,6-hexanedial, or to 1,6-hexanedicarboxylic acid. Each of these compounds contains two functional groups of the same kind. 

There is no simple way to disconnect the TM shown below (dissonant charge pattern). However, the presence of a 1,6-dioxygenated compound suggests opening of a six-member ring. A variety of cyclohexene precursors are readily available via condensation and Diels-Alder reactions or via Birch reductions of aromatic compounds. 

There is no synthetic equivalent for a carbonyl compound with a positively charged y-carbon, so we have to consider another route. Recognizing that a 1,6-dioxygenated compound can be prepared by oxidative cleavage of a cyclohexene provides an easy route to the target molecule, because a compound with a six-membered ring can be readily prepared by a Diels-Alder reaction. 

Dioxygenated compounds can be produced by ozonolytic cleavage of cyclohexenes different work-up procedures allow the differentiation of the termini of the product. Alternatively, cyclohexenes can be dihydroxylated and then cleaved with periodic acid or lead tetraacetate. 

The alcohol B is a typical amine-epoxide adduct, and the acid A is a 1,3-dioxygenated compound ... 

Analysis Disregarding the remote and unhelpful double bond, we can disconnect as a 1,3-dioxygenated compound (frames 94-107). 

Clearly other combinations of logical and illogical synthons could be used to make 1,4-dioxygenated compounds. How could you use cyanide ion (as the CO2H synthon) to make a y-keto acid such as... 

Review Problem 15 This triol (TM 192) can be taken as a 1,4- or a 1,5-dioxygenated compound. In fact only one of these will work. Suggest a synthesis. 

Analysis Our methods for making 1,2-dioxygenated compounds (frames 154-157) involve reductive linking of a dicarbonyl compound ... 

Unsymmetrical alkenes can be prepared from a mixture of two ketones, if one is in excess. " The mechanism consists of initial coupling of two radical species to give a 1,2-dioxygen compound (a titanium pinacolate), which is then deoxygenated. " ... 

In an elegant approach, Comba and co-workers initiated molecular-mechanics-based models that allow the rational design of ligand systems which are able to stabilize copper-dioxygen compounds. As a part of this investigation, complexes (241) (r = 0.12),223 (242) (r = 0.31),224 and (243) (r = 0.85)224 were synthesized and the reactivity of copper(I) complexes (Section 6.6.4.2.2(iv)) with dioxygen was investigated. 

The dithiane anion 1.9 also reacts with acyl halides, ketones and aldehydes to give the corresponding dioxygenated compounds. Schemes 1.4 and 1.5 show the reaction of dithiane anions 1.11 and 1.12 with ketones. The most common example of umpolung reactivity of a carbonyl group is the benzoin condensation (Scheme 1.6). 

Aldehyde 128 was also utilized for the preparation of the oxyrane 131, which gave, when reacted with the anion of the dithioacetal 129, 3,5-dioxygenated compounds such as 132 (111) (see preceding page). 

Dioxygenated compounds are formed similarly, except here it is often advantageous to exchange chloride for iodide before doing the triazole displacement. Cyclic... 

The hydrodeoxygenation reaction (HDO) is carried out in the gas phase in a fixed bed reactor (400 °C, 25 bar of hydrogen), using commercial nickel and molybdenum oxides supported on alumina as catalysts. The HDO allows a quantitative transformation of dioxygenated compounds into phenol with a selectivity of 96% [24]. Main by-products are heavy condensed polycyclic aromatic hydrocarbons. 

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