Catalyzed rearrangement oxidation

Synthesis of (A) started with the combination of 2,4,6-trimethylphenol and allyl bromide to give the or/Ao-allyl dienone. Acid-catalyzed rearrangement and oxidative bydroboration yielded the dienone with a propanol group in porlactone ring were irons in the product as expected (see p. 275). Treatment with aqueous potassium hydroxide gave the epoxy acid, which formed a crystalline salt with (R)-l-(or-naphthyl)ethylamine. This was recrystallized to constant rotation. 

Maltol. Otsuka Chemical Co. in Japan has operated several electroorganic processes on a small commercial scale. It has used plate and frame and aimular cells at currents in the range of 4500—6000 A (133). The process for the synthesis of maltol [118-71 -8], a food additive and flavor enhancer, starts from furfural [98-01-1] (see Food additives Flavors and spices). The electrochemical step is the oxidation of a-methylfurfural to give a cycHc acetal. The remaining reaction sequence is acid-catalyzed ring expansion, epoxidation with hydrogen peroxide, and then acid-catalyzed rearrangement to yield maltol, ie ... 

When position 4 of perfluoropyridine is blocked with a poor leaving group, ammonia replaces the fluonne in position 2 in good yield. Oxidation of the products obtained with hypochlorite, followed by lodme-catalyzed rearrangement, yields interesting fluorodienes [78] (equation 41) Ultraviolet irradiation can be used to assist reactions m which substitution is difficult [79]... 

Curran s synthesis of ( )-A9(l2)-capnellene [( )-2] is detailed in Schemes 30 and 31. This synthesis commences with the preparation of racemic bicyclic vinyl lactone 147 from ( )-norbomenone [( )-145] by a well-known route.61 Thus, Baeyer-Villiger oxidation of (+)-145 provides unsaturated bicyclic lactone 146, a compound that can be converted to the isomeric fused bicyclic lactone 147 by acid-catalyzed rearrangement. Reaction of 147 with methylmagne-sium bromide/CuBr SMe2 in THF at -20 °C takes the desired course and affords unsaturated carboxylic acid 148 in nearly quantitative yield. Iodolactonization of 148 to 149, followed by base-induced elimination, then provides the methyl-substituted bicyclic vinyl lactone 150 as a single regioisomer in 66% overall yield from 147. 

Similar to the thermal rearrangements discussed in the previous subsection, the base-catalyzed rearrangements of cyclic four-membered sulfones to five-membered sulfinates have also been reported. For example, Dodson and coworkers have observed the rearrangement of cis- and trans-2,4-diphenylthiethane 1,1 dioxides to cis- and trans-3, 5-diphenyl-1,2-oxathiolane (2,3)-cis-2-oxides, respectively (equation 35), on treatment with t-butoxymagnesium bromide, which is stereospecific with respect to the phenyl group but stereoselective with respect to the oxygen atoms on sulfur. 

Unintended EGA-catalyzed rearrangement of substrates during anodic oxidation has been reported in a number of cases, for example, rearrangement of strained polycyclic hydrocarbons upon oxidation in MeCN-LiCl04 [24]. 

These intrazeolite ene reactions are susceptible to many of the problems associated with photo-oxidations in solution. In particular, sensitizer bleaching, competition between type I vOi, and both type IIavRH and type 11 02 reactions, and reduced photostability of the products can complicate the synthetic use of these reactions [19]. In addition, many substrates are susceptible to acid-catalyzed rearrangements that can lead to complicated reaction mixtures. 

Caprolactam is discussed more completely in Chapter 11, Section 5. It is made from cyclohexane by oxidation to cyclohexanone-cyclohexanol mixture, formation of cyclohexanone oxime, and acid-catalyzed rearrangement. 

Butene is oxidized to methyl ethyl ketone, presumably arizing from the acid-catalyzed rearrangement of the peroxide. Alkenols and aldehydes are formed in lower amounts. Cyclopentene is more reactive towards oxidation than butenes. 

It has been pointed out (75TL213) that path A behavior might be more complex in some instances, and involve initial ylide formation followed by intramolecular proton abstraction (Scheme 202). The aryloxy quaternary salt (274), formed by reaction of pyridine 1-oxide with an arenediazonium salt, undergoes an interesting base-catalyzed rearrangement that is believed to take the course (path E) indicated (Scheme 203) (71JA3074). 

The Cope rearrangement of 24 gives 2,6,10-undecatrienyldimethylamine[28], Sativene (25j[29] and diquinane (26) have been synthesized by applying three different palladium-catalyzed reactions [oxidative cyclization of the 1,5-diene with Pd(OAc)2, intramolecular allylation of a /i-keto ester with allylic carbonate, and oxidation of terminal alkene to methyl ketone] using allyloctadienyl-dimethylamine (24) as a building block[30]. 

Campholenic Aldehyde Manufacture. Campholenic aldehyde is readily obtained by the Lewis-acid-catalyzed rearrangement of a-pinene oxide. It has become an important intermediate for the synthesis of a wide range of sandalwood fragrance compounds. Epoxidation of (+)- Ct-pinene (8) also gives the (+)-o -a-pinene epoxide [1686-14-2] (80) and rearrangement with zinc bromide is highly stereospecific and gives (-)-campholenic aldehyde... 

Direct oxidation of aromatics with m-CPBA in a two-phase system affords the most stable so-called K-region arene oxides in moderate yields.805 Careful control of pH is necessary to avoid acid-catalyzed rearrangement of the acid-sensitive product epoxides. The new powerful oxidants, dimethyldioxiranes,81,82 have also been used to convert arenes to arene oxides.806... 

The oxidation is carried out in the liquid phase, at relatively low temperature (90-120°C), pressure (5-7 atm), and conversion rate (20-40%) to achieve high selectivity. Cumene hydroperoxide is concentrated (70-85%) and then further converted. This second step includes an acid-catalyzed rearrangement and cleavage977 yielding phenol and acetone ... 

Cumene oxidized relatively slowly, at about 1/13 the rate of p-xylene. This was not caused by the formation of phenol, as might be expected by an acid-catalyzed rearrangement of cumene hydroperoxide. No phenol or product clearly derived from phenol, as by radical attack or by oxidation to a quinone, was detected at any time in the reaction mixture. The two major products were a-methylstyrene and 2-phenylpropylene oxide their concentrations increased with time. The group at Shell also observed the formation of a-methylstyrene and 2-phenylpropylene oxide among the products of cumene oxidation in butyric acid at 140°C. with cobalt and manganese catalysts (30). 

Synthetic methods for 2(5jF/)-furanones have been developed in the preparation of cardenolides (65MI31200). The ketone (171) when reacted with lithium ethoxyacetylide gives the carbinol (172) which undergoes acid catalyzed rearrangement to the a,/3-unsaturated ester (173). Allylic oxidation of (173) with selenium dioxide under mild conditions gives digitoxigenin acetate (174) (Scheme 38). 

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