Aldehydes flash vacuum pyrolysis

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). ... 

Aminotetrazole behaves like a normal primary amine in reactions with chloroform in base,328 phenyl isocyanate,328 p-toluenesulfonyl chloride,328 and aromatic aldehydes,43 and the expected derivatives of the amino moiety are obtained without interference at the tetrazole ring. With acid chlorides and anhydrides acylation of the amino group is accompanied by ring cleavage and yields 2-acylamino-1,3,4-oxadiazoles.43,328 Flash vacuum pyrolysis of 1 -phenyltetrazole at 500° has recently been reported to give phenylcyanamide as the only detectable product.333... 

Aliphatic or aromatic aldehydes react with (ethoxycarbonyliodomethyl)triphenyl-phosphorane (183) in the presence of potassium carbonate in a two-phase liquid-solid system to give acetylenic esters 184 . Pyrolysis of a-halophosphoranes 185 (X = Cl or Br R = Ar or t-Bu) results in 1-haloalkynes 186. Vacuum pyrolysis of the betaine 188, formed from the phenoxymethylenephosphorane 187, yields the acetylenic ether 189 Flash-vacuum pyrolysis of the phosphorane 190 at 750°C gives triphenylphosphine oxide and phenylacetylene with elimination of the ethoxycarbonyl groups... 

Addition reactions of (l-methoxyalkyl)triphenylphosphonium ylides, derived from the corresponding phosphonium salts (82) and n-BuLi, to aldehydes at — 78 °C followed by quenching the reaction mixture with aqueous NH4CI at the same temperature alforded a-hydroxyketones instead of the expected enol ethers.This is the first example of phosphonium ylides acting as an acyl anion equivalent. Flash vacuum pyrolysis (FVP) in a conventional flow system at 10 (84), prepared in a few steps... 

Pohmakotr et al. have developed a general and convenient method for the synthesis of 2-(hydroxyalkyl)-5-methylenecyclopentenones 377 via the MBH reaetion of a masked 5-alkylidene-2-cyclopentenone (375) with aldehydes, eatalyzed by tributylphosphine in the presence of phenol, to provide the corresponding MBH adducts 376, followed by the flash vacuum pyrolysis (FVP) to give the resulting adducts 377 (Scheme 2.209). ... 

Pyrolysis of pyridine derivatives is a method for allylic and benzylic deamination the preparation of nitriles from aldehydes, and the preparation of isocyanates from acid chlorides or hydrazides Flash vacuum pyrolysis continues to yield interesting reactions and products. Recently, it has been reported that quite sensitive acetylene derivatives can be obtained by this method from 4-alkylideneisoxazol-5(4H)-ones by ring degradation. On the other hand, 2 carbamyl azide molecules cyclize under these conditions to form l,2,4-triazolidine-3,5-dione 1,2-ylids . 2H-Cyclohepta[b]furan-2-ones have been obtained by ring expansion of phenyl propiolates... 

Flash vacuum pyrolysis of primary Al-alkoxyphthalimides at 400—500 °C and 0.02 Torr has provided functionally substituted aldehydes. On the basis of the kinetic data and product analysis, a mechanism involving a six-membered TS has been proposed. 

Flash vacuum pyrolysis of 4-methylene-5-oxo-4,5-dihydro-l,2-oxazoles (93) at 700—800 C gives terminal acetylenes in good yield, provided that (93) is volatile and stable at this temperature. Thus a range of heteroaromatic aldehydes can be converted into the corresponding homologous acetylenes by this route. 

The origin of the observed products, mainly indanone, hydroxyalkynes, and a, -unsaturated aldehydes, from the flash vacuum pyrolysis of pyrazolinones, has been... 

Similarly, the reaction of PhSCF2SiMe3 with aldehydes and ketones using 10 mol % of anhydrous tetra-n-butylammonium fluoride (TBAF) reported by Pohmakotr et al. also provided the corresponding adducts, both carbinols and silyl ethers, in moderate to excellent yields (39-92%). The silyl ethers could be converted into the corresponding carbinols in quantitative yields by using KF in acetonitrile/THF (eq 4). Subsequent oxidation of the carbinol sulfides to sulfoxides followed by flash vacuum pyrolysis (FVP) gave the corresponding e/n-difluoroalkenes in 41-82% yields (eq 5). ... 

Form Supplied in colorless liquid not commercially available. Analysis of Reagent Purity IR (tf) 2955,2900,1935,1250,1210, 1055,840,800,750, and 690 cm H NMR (60 MHz, CDCI3) 50.15 (s, 9H),4.27 (d, 2H, /= 7.7),4.88 (dd, IH,7= 6.6,7.7). Preparative Method two methods have been reported for the preparation of (trimethylsilyl)allene [(TMS)allene] (1). Reductive deoxygenation of the tosylhydrazone derivative affords the title compound in 51% yield. The tosylhydrazone is readily prepared from the corresponding aldehyde, which in turn is accessed by formylation of (trimethylsilyl)ethynylmagnesium bromide with DMF (eq 1). (TMS)allene has also been prepared by flash vacuum pyrolysis of methyl (trimethylsilyl)-propargyl ether, which is obtained from silylation of methyl propargyl ether (eq 2)7... 

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