Reaction with dihydro-1,4-dioxane

The 6,7-dihydro-5/f -1,4-dioxepin (266) has been prepared (54CR(38)982). and more recently it has been shown that the 2,3-dihydro-5jF/-l,4-dioxepins (263) and (265) can be produced from 1,4-dioxine-halocarbene adducts (264), either by heating under reflux in xylene or by treatment with bases. The allylic chlorine atom in (263) is readily substituted by alkoxide or cyanide ions (77ZC331, 76UKZ968). Saturated rings of type (267) have been prepared by the treatment of cyclic acetals of ethane-1,2-diol with vinyl ethers in the presence of boron trifluoride, and l,4-dioxepan-5-one (268) has been prepared by the reaction of bromoform and silver nitrate with aqueous dioxane (60AG415). 

An improved synthesis of glutinosone (1) was also accomplished by Masamune and coworkers6 and this was based on procedure developed by Dastur7,8 for the synthesis of sesquiterpenes nootkatone. (Scheme 2) Diels-Alder reaction of 3,6-dihydro-3,5-dimethyl anisole with methyl acrylate in absence of Lewis acids afforded a 1 3 mixture of esters (17) and (18) which were converted to a,(3-unsaturated aldehydes (19) in 77% yield by oxidation with selenium (IV) oxide in dioxane. Wittig reaction of aldehydes under the usual condition yielded the dienes (20) in 63% yield which on being subjected to Grignard reaction with an excess of methyllithium produced tettiary alcohols (21) in quantitative yield. This on treatment with formic acid at room temperature gave bicyclic enone (22) and its formate (23) in 45% and 41% yield respectively. Formates (23) were hydrolyzed to enone (22) in 88% yield. 

By contrast, in the reaction in refluxing dioxan of the substituted butyrolactone shown with 2-methyl-4-benzoyloxyphenol in the presence of boron trifluoride etherate until completion, 2-(6-benzoyloxy-3,4-dihydro-3,8-dimethylbenzopyran-2-yl)propionic acid was obtained (ref.180). Acylation was not observed. 

Reaction of 8,9-difluoro-5-methyl-6,7-dihydro-5//-pyrido[3,2,l-//]quina-zoline-l,3-dione with 2,4-dinitrophenylhydroxylamine in the presence of NaH in a 1 1 mixture of dioxan and DMF at 60-80 °C afforded 2-amino derivative (01MIP23). 

ICj Preparation of 3-Bemyl-6-Trifluoromethyl-7-Sulfamyl-3,4-Dihydro-1, 4 Ben othiadiazine 1,1-Dioxide A grams of 5-trifluoromethyl-2,4-disulfamylaniline is dissolved in 12 ml of dioxane. 2.7 ml of phenylacetaldehyde and a catalytic amount of p-toluenesulfonic acid are added. After boiling for a short time under reflux, the reaction mixture crystallizes, and, after filtration and recrystallization from dioxane, the desired product is obtained with a MP of 224.5°-225.5 C,... 

A mixture of 4.9 grams of 5,6-dihydro-6-oxo-morphanthridine, 37 ml of phosphorus oxychloride and 1.5 ml of dimethylaniline Is heated for 3 hours at reflux. The viscous oil, obtained by evaporation of the reaction mixture in vacuo at 60°C, Is diluted with 20 ml of absolute dioxane and, after adding 30 ml of N-methylpiperazine, heated for 4 hours at reflux. The resulting clear solution Is evaporated in vacuo at 60°C to dryness. The residue is distributed between ether and ammonia water. The ethereal solution is separated, washed with water and then extracted with 1 N acetic acid. The acetic acid extract is mixed with ammonia water and then extracted with ether. The ethereal solution is washed with water, dried over sodium sulfate, filtered through alumina and evaporated. 

Cyclopenta[fc]dioxanes (44) are accessible from the reaction of the dioxenylmolybdenum carbene complex (43) with enynes <96JOC159>, whilst an intramolecular and stereoselective cyclisation of (Ti5-dienyl)tricarbonyliron(l+) cations affords chiral frans-2,3-disubstituted 1,4-dioxanes <96JOC1914>. 2,3-Dimethylidene-2,3-dihydro-1,4-benzodioxin is a precursor of the 3,8-dioxa-lff-cyclopropa[i]anthracene, which readily dimerises to dihydrotetraoxaheptacene (45) and the analogous heptaphene <96AJC533>. 

Bicyclic lactams 189 are uniquely suited as precursors for the synthesis of chiral substituted 4,5-dihydro-277-pyridazinones 190 by hydrolysis with NH2NH2 and HC1 in dioxane at 85 °C. The reaction gave, as a side product, the ketoacid 191 in some cases (Equation 32) <2003TL7997>. 

Synthesis of 2,3-dihydro-l,4-dithiin 11 was accomplished from l,3-dithiol-2-one 247 in the presence of dibro-moethane and potassium hydroxide <1998JOG3952>, while reaction of 2,3-dichloro-l,4-dioxane with powdered Zn in hexamethylphosphoramide (HMPA) was used for the synthesis of 1,4-dioxene 10 <1998JPP10067773>. To obtain substituted 1,4-oxathianes, the hydrogenation of the corresponding partially saturated compounds has been employed <2001J(P1)2604>. 

Functionalised 2,3-dihydro-l,4-dioxins can be synthesised in a three step-sequence from P-keto esters. The key step is the insertion of a Rh-carbenoid derived from an a-diazo-p-keto ester into an 0-H bond of a 13-diol <99H(51)1073>. The reaction of 2-(l,4-dioxenyl)alkanols with silyl enol ethers yields 23-disubstituted 1,4-dioxanes. When 13-bis(trimethylsilyloxy)-cyclobut-l-ene is used, the expected cyclobutanone products are accompanied by a spirocyclopropane derivative <99TL863>. 1,4-Dioxane-monochloroborane 57 is a highly reactive hydroborating reagent <990L315>. 

Acy 1-4-amino-1,5-dihydro-2-pyrrolones (6) (type Z in Scheme 1) possess the features of cyclic enaminediones. The push-pull-7r system decreases the nucleophilicity of the amino group. Therefore N-acylation with carboxylic acid chlorides requires relatively drastic conditions (dioxane, 100°C, K2C03). In particular, the reaction of the highly reactive DMF-acetal 8 to formamidine 9 succeeds only while refluxing in benzene (87TH1). (See Fig. 3.)... 

Dihydro-4-methylcyclopent[b]indol-l(2H)-one oxime (1.53 g), polyphosphoric acid (409 g) and dioxan (15 ml) were heated at 110-120°C for 2.2 h under nitrogen. The reaction mixture was cooled, and treated with 2 N sodium carbonate solution (1 L). The suspension was extracted with ethyl acetate (4x400 ml) and the combined extracts were dried. Evaporation gave a solid (1.43 g) which was recrystallised from ethyl acetate/cyclohexane. This solid was purified by FCC, eluting with dichloromethane ethanol ammonia solution (200 10 1) to give a solid (1.26 g) which was recrystallised from ethanol to provide the title compound (960 mg), m.p. 234-238°C. 

A mixture of 30 parts of 4-[4-(4-methoxyphenyl)-l-piperazinyl]benzenamine and 300 parts of a hydrobromic acid solution 48% in water is stirred and refluxed for 10 days. The reaction mixture is evaporated and the residue is alkalized with sodium hydroxide. The mixture is filtered and the filtrate is acidified with acetic acid. The precipitated product is filtered off and crystallized from 1,4-dioxane, yielding 12 parts (44%) of 2,4-dihydro-4- 4-[4-(4-hydroxyphenyl)-l-piperazinyl]phenyl -2-(l-methylpropyl)-3H-l,2,4-triazol-3-one. 

The total synthesis of ( )-xenovenine 100 ° was carried out by applying the present cyclization reaction as shown in Scheme 47. Closure of oxime 98j proceeded successfully by treatment with NaH, sesamol 97, and 1,4-cyclohexadiene in 1,4-dioxane at 50 °C, giving 3,4-dihydro-2f/-pyrrole 99j in 87% yield. 

BF3 Et20 is useful for the condensation of allylic alcohols with enols. A classic example is the reaction of phytol in dioxane with 2-methyl-l,4-naphthohydroquinone 1-monoacetate to form the dihydro monoacetate of vitamin Ki (Eq. 30), which can be easily oxidized to the quinone [57]. 

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