Double bond-cleavage

Oxidation of olefins and dienes provides the classic means for syntheses of 1,2- and 1,4-difunctional carbon compounds. The related cleavage of cyclohexene rings to produce 1,6-dioxo compounds has already been discussed in section 1.14. Many regio- and stereoselective oxidations have been developed within the enormously productive field of steroid syntheses. Our examples for regio- and stereoselective C C double bond oxidations as well as the examples for C C double bond cleavages (see p. 87f.) are largely selected from this area. 

This two-step sequence is a valuable alternative to the direct double bond cleavage by ozonolysis. 

The keto group must come from double bond cleavage so we may add anything we please as R in (17), The obvious choice is hydrogen as (17) can then be made by a Wittig reaction on available aldehyde (18). 

Wyss, A., Carotene oxygenases a new family of double bond cleavage enzymes, J. Nutr. 134, 246S, 2004. 

J. Tercio, B.Ferreira, W. O. Cruz, P. C. Vieira, andM. Yonashiro, Carbon-carbon double bond cleavage using solid-supported potassium permanaganate on silica gel, J. Org. Chem., 52 (1987) 3698-3699. 

This compound chemiluminesces when exposed to air or oxygen. Its CL was first demonstrated by Fletcher and Heller [47, 48] and suggested to occur via formation of a dioxetane by addition of oxygen across the ethylenic double bond. Cleavage of the dioxetane to form excited tetramethylurea results in excitation of the tetrakis (dimethylamino) ethylene, whose CL is in good agreement with the fluorescence spectrum of the parent compound. The reaction has been used for the analysis of oxygen [49, 50],... 

Scheme 56 Double-bond cleavage with osmiumtetroxide/periodate.

The electrocatalytic oxidation of styrene with molecular oxygen in the presence of CuCh in an acetonitrile solution promotes the C=C double-bond cleavage reaction... 

Fig. 8. Ru porphyrin/TBHP-catalyzed double bond cleavage.

There is some information concerning the reaction of ozone with chemicals under aqueous conditions. The information available suggests that double-bond cleavage takes place, just as it does under nonaqueous conditions, except that ozonides are not formed. Instead, the zwitterionk intermediate reacts with water, producing an aldehyde and hydrogen peroxide. In addition to double-bond cleavage, a number of other oxidations are possible. Mudd et showed that the susceptibility of amino acids is in the order cysteine, tryptophan, methionine. 

This approximate fivefold excess is necessary to reduce flic chromium higher valent salts and thereby eliminate overoxidation and double bond cleavage. The zinc dust used was obtained from Allied Chemical Corporation. 

I n contrast to the relative simplicity of the chromyl chloride oxidation of 2,2-disubstituted-l-alkenes to aldehydes, the rlimmyl acetate and chromic acid oxidations generally lead to epoxides, acids, and carbon-carbon double bond cleavage. For example, chromyl acetate oxidizes 4,4-dimethyl-2-neopentyl-I pentene primarily to l,2-epoxy-4,4-dimethyl-2-neopentyl-pentane in low yield,9 and chromic acid oxidizes the alkene principally to 4,4-dimethyl-2-neopentylpentanoic acid.6,10... 

The catalytic system tranx-[Ru(0)2 (105(0H) 3] /K(I0 )/aq. KOH or aq. Aliquat converted primary alcohols [554, 555] and primary activated alkyl halides [555] to carboxylic acids, while secondary alcohols [554, 555], and secondary alkyl halides were oxidised to ketones [555]. As with catalytic oxidations by aqueous [RuO ] double bond cleavage occurs [555]. 

The system [Ru(0)3Cl3] /NM0/PMS/CH3Cl2 oxidised primary alcohols to aldehydes and secondary alcohols to ketones without competing double-bond cleavage... 

The carbon-carbon double-bond cleavage is accessible also with the MTO/H2O2 sys-tem . By tuning the reaction conditions it was possible to obtain, for a given substrate,... 

SCHEME 1. Types of alkene and alkyne metathesis reactions. DBC, double bond cleavage TBC, triple bond cleavage ADMET, acyclic diene metathesis RCM ring-closing metathesis ROMP ring-opening metathesis polymerization... 

In the oxidation of indene, where the double bond is located in the five-membered ring (entry 3), the preference of oxygen for the a-position is even more pronounced, with the ratio of a- to P-indanone being 4.5 1. Presumably, 2-ethenylbenzaldehyde (10%) forms as a result of double bond cleavage. 

Double Bond Cleavage under an Ozonization-Electroreduction... 

Electrochemical reduction of the ozonization products from monoterpenes, i.e., />-meth-l-ene, (-l-)-limonene, (+ )-a// /ia-pinene, (+)-car-3-ene, provides the corresponding double-bond cleavage products in 45-70% yields57. The electrolysis of the acetyloxy hydroperoxide 28 derived from p-menth-l-ene 27 is carried out in an Ac0H/H20(6/1 v/v)— AcONa— (Pb/Pb) system at —1.1 to —1.4V vs. SCE, 2.0 to 2.2 A/dm2 in a divided cell to give the corresponding keto-alcohol 29 in 70% yield (Scheme 3-10). 

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