Quinones vinyl substitutions

Hemmingson, J. A. Leary, G. The chemistry of reactive lignin intermediates. Part II. Addition reactions of vinyl-substituted quinone methides in aqueous solution. J. Chem. Soc., Perkin Trans. 1975, 2, 1584-1587. 

Several other heterocyclic compounds have been used in the vinyl substitution. Quinones, for example, are readily substituted with a variety of heterocycles as well as with benzene.7 Heterocycles which react include 2-acetylfuran (5-position), furfural (5-position) (equation 5) methyl furoate (5-position), 2-ace-tylthiophene (5-position), N-benzenesulfonylpyirole (2-position), N-benzenesulfonylindole (3-position), 4-pyrone (3-position) and N-methyl-2-pyridone (3- and 5-positions). 

Cavaleiro et al. reported the reaction of vinyl-substituted zinc porphyrins 76 with Knoevenagel products of formaldehyde 72 with several quinones 75 in refluxing 1,4-dioxane and ort/jo-dichlorobenzene (Scheme 13.22) [37]. The desired products 77 could be obtained in moderate to high yields where the exclusive formation of the para-benzoquinone is noteworthy (see also [36]). A catalytic amount of acetic acid reduces the reaction time and increases the product yield. 

Quinone Methides. The reaction between aldehydes and alkylphenols can also be base-cataly2ed. Under mild conditions, 2,6-DTBP reacts with formaldehyde in the presence of a base to produce the methylol derivative (22) which reacts further with base to eliminate a molecule of water and form a reactive intermediate, the quinone methide (23). Quinone methides undergo a broad array of transformations by way of addition reactions. These molecules ate conjugated homologues of vinyl ketones, but are more reactive because of the driving force associated with rearomatization after addition. An example of this type of addition is between the quinone methide and methanol to produce the substituted ben2yl methyl ether (24). 

Oxidation of the o/T/zo-substituted acetanilides 324 with DMP leads to the isolable o-iminobenzoquinones 325 (Scheme 94) (02JA2221). The imino-quinones undergo inverse electron demand Diels-Alder reactions with the vinyl ether and vinyl sulfide shown in Scheme 94, thus providing access to the benzoxazine derivatives 326 and 327. 

The thermal and photochemical [4 + 2] cycloadditions of o-quinones with olefinic and acetylenic dienophiles have been extensively reviewed4,5,200 and include their 4tt heterodiene Diels-Alder reactions with olefins,201-204 vinyl ethers,205 enamines,206 selected dienes,207-209 dipheny-lketenimines,210 ketenes,209,210 fulvenes,211 and selected heterocycles including furan,207-209,212 benzofuran,209,212,215 indoles,213 azepines,214 and 1,2-diazepines.214 The tetrahalo-substituted o-quinones, tetrachloro- and tetrabromo-o-quinone, generally participate in heterodiene [4 + 2] cycloadditions at an increased rate over the unsubstituted systems and generally provide higher overall yields of the Diels-Alder products.4,5 With simple olefins, the dienophile geometry is maintained in the course of the thermal [4 4- 2] cycloadditions [Eq. (52)],203,204... 

Phosphoranylideneaminoquinones, e.g. (20), have been prepared in good to excellent yields by the reaction of phosphines with [2,l]benzisoxazole-4,7-quinones, e.g. (19)." A safer alternative to the vinyl azide-based synthesis of (N-vinylimino)phosphoranes (21) has been reported (Scheme 1)." N-(AlkyIthiomethyl)iminophosphoranes (23) have been synthesised from the benzotriazole-substituted iminophosphorane (22) and used without isolation to provide routes to N-alkylthiomethyl-imines, -amides, and -ureas. Tetraazolyl-substituted ylides (25) and (26) are the products of the reaction of vinylphosphonium salts (24) with excess sodium azide." The novel 1,2-1 -azaphosphete (28), which is potentially antiaromatic, has been prepared by the reaction of the azide... 

Diels-Alder Reactions. Bp3-OEt2 is used to catalyze and reverse the regiospecificity of some Diels-Alder reactions, e.g. with pen-hydroxylated naphthoquinones, sulfur-containing conpounds, the reaction of 1-substituted trans-1,3-dienes with 2,6-dimethylbenzoquinones, and the reaction of 6-inethoxy-l-vinyl-3,4-dihydronaphthalene with p-quinones. BFs-OEta has a drastic effect on the regioselectivity of the Diels-Alder reaction of quinoline- and isoquinoline-5,8-dione with piperylene, which produces substituted azaanthraquinones. This Lewis acid is the most effective catalyst for the Diels-Alder reaction of furan with methyl acrylate, giving high endo selectivity in the 7-oxabicyclo[2.2.1]heptene product (eq 35). ... 

Lee et al. found that the DABCO-catalyzed MBH reaction between methyl acrylate and methyl vinyl ketone with 2,3-dihalo-1,4-naphthoquinone 60 forms a-vinylnaphthoquinones in moderate to good yields. The same authors subsequently reported additional examples of the use of DABCO attached enolate anion of methyl acrylate and MVK in substitution reactions of halo-quinones to form a-vinylquinone bonds, avoiding the use of organometallic reagents (Scheme 2.26). ... 

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