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Bicyclic ortho esters

Carboxylic acids can also be protected as ortho esters. Ortho esters derived from simple alcohols are very easily hydrolyzed, and a more useful ortho ester protecting group is the 4-methyl-2,6,7-trioxabicyclo[2.2.2]octane structure. These bicyclic orthoesters can be prepared by exchange with other ortho esters, by reaction with iminoethers, or by rearrangement of the ester derived from 3-hydroxymethyl-3-methyloxetane. [Pg.838]

The use of 1,2- and 1,3-diols in the transesterification reaction provides a means of providing monocyclic ortho esters [49-54]. Cycloalkanediols or acyclic triols result in bicyclic [55] and polycyclic ortho esters [56, 57] (Eqs. 22, 23). [Pg.286]

Reaction of dihalo- and trihaloacetic acid and a,a-dihalopropionic acid with trimethylolethane (2-hydroxymethyl-2-methyl-l,3-propanediol) to give bicyclic ortho esters [204]. [Pg.292]

As a result, the stereoregular polymerization of VI and VIII has not succeeded. Form the above findings we can give a rough-hewn conclusion for the polymerization of bicyclic ethers, acetals, and ortho esters as is shown in Table 6. [Pg.132]

C-IS in 55% yield (Scheme 53). In this case, the thermal Claisen rearrangement occurred stereospecifi-cally from the a-face of the bicycle, presumably via chair transition state (309) (Scheme 54). Therefore it was concluded that the ortho ester rearrangement occurred predominantly via boat transition state (310), providing the first example of a difference in transition state geometry observed in Claisen variants with the same substrate. [Pg.865]

Synthesis and Polymerization of Atom-Bridged Bicyclic Acetals and Ortho Esters... [Pg.313]

Oxazolo[2,3-fe]oxazoles (191 R = CF3, n-C7F,5) have been prepared by acid-catalyzed dehydration of A,A-bis(hydroxyalkyl)amides <82JFC(2l)359>. The imidazo[l,5-6f]imidazole (193) was prepared by reaction of aminoacetonitrile with excess trimethylorthoformate in the presence of catalytic amounts of formic acid <84JOCl2i2>. The reaction is believed to involve the initial formation of the imidate (192) which reacts successively with aminoacetonitrile and the ortho-ester to give the observed product. Pyrazolo[5,l-Z>]oxazoles (198) have been synthesized by reaction of hydrazino alcohols (195) with the Michael adduct (194), prepared from A-isobutylidene-r-butylamine and dimethyl-methoxymethylene malonate <93JHC1529>. The reaction is believed to involve cyclization of the intermediate hydrazones (196) to give pyrazoles (197), which subsequently cyclize to the bicyclic system with loss of dimethyl malonate. [Pg.118]

Cyclising condensation of ortho-acylaryloxy- or -arylthioacetic acids (esters) or ketones gives the bicyclic heterocycles. [Pg.386]

Coyle has summarized the photochemistry of carboxylic acid derivatives. For arene carboxylic acid esters it has been shown that [2-1-2]-cycloaddition competes with hydrogen abstraction by the excited ester from an allylic position of the alkene. The addition of methyl benzoate 17 to 2-methyl-2-butene gave a 1 1 mixture of the Paterno-Bilchi adduct 18 and the coupling product 19. Less electron-rich alkenes (e.g., cyclopentene) did add preferentially toward the benzene ring of 17 in an ortho- and metacycloaddition manner. Furans could also be added photochemically to methyl benzoate and other aren-ecarboxylic acid esters. The resulting bicyclic oxetanes could be transformed into a series of synthetically valuable products. [2-1-2]-Cycloadducts and/or their cleavage or rearrangement products have also been described for photoreactions of alkenes with diethyl oxalate,benzoic acid, " and carbamates. ... [Pg.1239]


See other pages where Bicyclic ortho esters is mentioned: [Pg.40]    [Pg.40]    [Pg.595]    [Pg.131]    [Pg.133]    [Pg.989]    [Pg.193]    [Pg.989]    [Pg.459]    [Pg.11]    [Pg.237]    [Pg.170]    [Pg.94]    [Pg.910]    [Pg.1245]    [Pg.262]    [Pg.156]    [Pg.52]   


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Ortho esters

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