Naphthols, methylene derivatives

An interesting route to a-carboxy-8-lactones (81) and a-methylenelactones (80), based on hydrolysis of Knoevenagel products (79) of Meldrum s acid with cyclic aliphatic ketones (78), has been developed (Scheme 14). Reduction of 5-methylene derivatives of Meldrum s acid has been performed catalyti-caiiyi30 or by use of LAH. Imidoylation reaction of Meldrum s acid and subsequent solvolysis of the resulting (82) yields -enamino esters (83) in good yields.Flash vacuum pyrolysis of alkylidene derivatives of Meldrum s acid can be used to prepare methylene ketenes (84), a class of compounds difficult to prepare by conventional methods. By this procedure, methylene ketenes are obtained from aromatic aldehydes and ketones and from aliphatic ketones in only two steps. Intramolecular trapping of the methylene ketene obtained from the ketone (85) has been used successfully in the synthesis of the naphthol (86). ... 

A solvent-free synthesis of substituted spiroindolinonaphth[2,l-fo][l,4]oxazines through condensation of 2-methylene-l,3,3-trimethylindoline derivatives with 1-nitroso-2-naphthol under microwave irradiation has been described by Fedorova and colleagues (Scheme 6.263) [453], In a typical reaction, an equimolar mixture of the two starting materials was irradiated at 65-110 °C for 15 min to produce the desired spiroindolinonaphth[2,l-fo][l,4]oxazines, which are useful as photochromic compounds. In a related procedure, addition of morpholine to the reaction mixture led to the formation of the corresponding 6 -amino-functionalized spiroindolino-naphth[2,l-fo][l,4]oxazines, which exhibit a strong hypsochromic color shift (not shown) [453]. 

Novel -symmetric chiral arsepin 61 possessing the 1,1 -binaphthyl-2,2 -bis(methylene) backbone was prepared using (S)-(—)-l,l -bi-2-naphthol 84 as the chiral substrate. The dilithio derivative 86, generated from (S)-2,2 dimethyl-1,1 -binaphthyl 85 and Avy-biitvllithiuru, reacted with PhAsBr2 to give arsepin 61 (Scheme 7) <2002TA2187>. 

Coupling with phenols is usually effected more easily than coupling with amines, and naphthols couple considerably more readily than hydroxybenzene derivatives. Reactive methylene compounds behave similarly to phenols of the benzene series. Negative substituents (halogen, nitro, sulfo, carboxyl, carbonyl, etc.) accelerate coupling when... 

A mixture of Meldrum s acid or barbituric acid derivatives, urea and aldehyde gave 99, stereoselectively. Reaction of 2-methylene indoline derivatives with l-nitroso-2-naphthol gave 100. Spiroheterocycles 101 were prepared from a mixture of isatin and aromatic or heterocyclic... 

Condensation of 2-methylene indoline derivatives 816 with l-nitroso-2-naphthol (817) under MWI gave spiro indolinonaphth[2,l-6][l,4]oxazines 818 in 11-61% yields within 12 min. When the same reaction was carried out in the presence of morpholine, 819 were also formed in 19-34% yields (Scheme 155) (04SC315). 

The synthesis of 2-aminochromes by Vaddula and Gonzalez [77] is an example of a multicomponent reaction performed within a single pass of a continuous-flow ThalesNano H-Cube Pro reactor. Using this reactor the authors demonstrated that various chromene derivatives could be obtained with a simple and rapid one-step continuous-flow synthesis route from the reaction of aromatic aldehydes, a-cyano-methylene compounds, and naphthols. The efficient, safer, faster, and modular reaction proceeded to completion with very high yields and residence times of less than 2 min at a slightly elevated pressure of approximately 25 bar. 

Pyrolysis of the Meldrum acid derivative 458 produces the methylene ketene 459, which rearranges to the dienylketene 460 while the latter undergoes cyclization to give the /3-naphthol 461 . 

Although these generaliaations furnish a satisfactoi picture of the efiiect of alkali and add on most phenol-formaldehyde reactions, the structure of the phenols involved is sometimes of paramount importance and may result in defimte exceptions to general rules. Ortho-nitrophenol forms methylol derivatives under acidic conditions and beta naphthol gives a quantitative yield of methylene bis-beta-uaphthol in the presence of alkaline catalysts. 

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