Methyl-2- ketene

On this basis it was reasoned that a benzyl group in a ketene acetal should greatly increase the extent of cleavage during polymerization and, therefore, should increase the efficiency of chain transfer. That in fact is what occurred when an equimolar mixture benzyl methyl ketene acetal (XIV) and styrene was heated at 120°C in the presence of di-tert-buty1 peroxide an oligomer with 80% styrene units and capped with a carbomethoxy group was obtained. 

Ketene itself and simple alkylketenes are inert towards nonactivated alkenes. F or the preparation of cyclobutanones formally derived from ketene or an alkylketene and nonactivated alkenes, the more reactive dichloroketene or alkylchloroketenes can be used. The corresponding a,a-dichloro- or oc-chlorocyclobutanones can readily be dechlorinated by treatment with zinc in acetic acid, or tributyltin hydride in near quantitative yields. F or example cycloaddition of substituted cyclohexene to dichloroketene gave dichlorocyclobutanone 1 which was dechlorinated to 2 with zinc.13,18 Likewise cycloaddition of cycloalkcnes to chloro(methyl)ketene gave 3 which was dechlorinated to 4.14... 

For 5-alkylidenetetrazolines (33) three reaction paths have to be considered. They afford either N-methyl ketene imines and methyl azide, or, in addition to molecular nitrogen, a 3-alkylidenediaziridine (least-motion path) or a methyliminoaziridine (non-least-motion path). As was shown by... 

When iV-methyl ketene aminals 244 reacted with ethyl propiolate in 1 1 mole ratio, 1,2,3,4-tetrahydro-6//-pyrido[l, 2-a]pyrimidin-6-ones 245 were obtained as the main products (35-58%) together with a low yield of (6-oxo-6//-pyrido[ 1,2-a]pyrimidin-7-yl)acrylates 246 (5-7%) [93JCS(P1)-... 

The ester side chain is introduced via 1,4-conjugate addition of tert-butyldimethylsilyl methyl ketene acetal (12) to the ,/Tunsaturated ketone. Here 11 is stirred in a 2.0 M solution of lithium perchlorate (LiC104) in diethyl ether together with 12 for 1 h at room temperature. A large excess of both reagents is necessary (25 equiv. LiCI04 and 10 equiv. 12).18... 

Scheme 1.3 Pracejus enantioselective ester synthesis from phenyl methyl ketene.

The preference for a chairlike transition state in the Johnson-Claisen rearrangement is supported by further Houk et al. s computational studies (Scheme 1.2e).5 For the rearrangement of the parent methyl ketene acetal, chairlike transition state A is favored over boatlike transition state B by 2.3 kcal/mol. 

Chloro[(trimethylsilyl)methyl]ketene. Formaldehyde. Titanocene methylene-Zinc halide. 

METHYLENECYCLOALKANES 2,4,6-TliisoprO-pylbenzenesulfonyl hydrazine. a-METHYLENECYCLOBUTANONES Chloro-[(trimethy lsily l)methyl]ketene. METHYLENECYCLOPENTANES 4-Chloro-2-lithio-1-butene. 

Thermal reaction of larger carboxylic acids on titanium dioxide surfaces traced reaction pathways similar to those of formic acid. The (110 -faceted surface of TiOiCOOl) selectively decomposed acetate and propionate via unimolecular dehydration to form ketene and methyl ketene. The dehydration yields from both reactants were quite similar, as were the desorption temperatures of the products [46]. 

Acetic acid decomposed on the (114[-faceted of the TiOi (001) surface to produce ketene as well as acetone [44]. The acetone generated arose from bimolecular coupling of pairs of surface acetates at four-fold coordinate cations this is analogous to the production of formaldehyde from surface formate on identically prepared surfaces. The reaction of propionic acid corresponded directly to the reaction of acetic acid, producing methyl ketene and 3-pentanone [46]. 

According to Blake and Hole , methyl ketene decomposes into CO2 and pentadiene-2,3 as well as into CO and butene-2 subsequent polymerization and decomposition processes produce other products, especially at higher temperatures. The results indicate that the overall orders of both CO2 and CO formation are 1.5 and each reaction path is inhibited by isobutene. Blake and Hole suggested tentative chain mechanisms to account for the observed product formation and for the kinetics of the decomposition. Initiation and termination was assumed to occur at the surface of the vessel. 

The analogous reaction paths and the similar overall kinetics of the pyrolyses of ketene and methyl ketene seem to suggest more similarities in the mechanisms than is assumed at present. A detailed examination of this point could be profitable. 

Fo-p-silylcyclobutanone precursor (135) was prepared by an efficient [2 + 2] cycloaddition of chloro[(tri-methylsilyl)methyl]ketene (134) with 3,4-dihydro-2//-pyran. 

Dimethylketene reacts in the same way and gives 148, whereas methyl-ketene gives the enolester (149).212 The reaction of diphenylketene with 1,2-dithiole-3-thiones occurs with loss of the thiocarbonyl sulfur213 (e.g., 150). It is suggested that this reaction proceeds via the normal 1,3-dithiolane derivative.211... 

Formation of 5-methyltricyclo[3.3.0.0 ]oct-6-en-3-one (1) by thermal decomposition of l-diazo-3-(l-methylcyclopenta-2,4-dienyl)propan-2-one succeeded remarkably well. It is worth noting that the Wolff rearrangement leading to [(l-methylcyclopenta 2,4-dienyl)methyl]ketene is of no importance, in contrast to the direct, unsensitized irradiation of the diazo compound (see Section 1.2.1.2.4.2.6.2.). 

Thus, 2-bromo-2,3,4-trimethylcyclobutanone, the adduct of bromo(methyl)ketene and (Z)-but-2-ene, on treatment with sodium methoxide in methanol, underwent rearrangement into 2-methoxy-2,3,4-trimethylcyclobutanone (10) in 70% yield. S A mechanism involving a -enolization, followed by methoxy substitution and subsequent loss of the a-halogen was proposed to take this unexpected result into account. For other reported cine substitutions, see refs 14, 36 and 50. 

N-Phenyl-methyl-ketene imine N-1 -propenylideneaniline) (189) Carbon chemical shift 386. 

Oxathietan 1,1-dioxide (130) reacts with alcohols to give (2-fluorosulphonyl)-carboxylic esters, and with BFj and EtjN to give fluorosulphonyl(trifluoro-methyl)keten. The latter reaction is more efficient if the ring is first opened with KF and HF. Chloral cyclo-adds to sulphenes to give yff-sultones. 4-Tri-chloromethyl-l,2-oxathietan 2,2-dioxide reacts with primary and secondary amines to give y5-hydroxy-sulphonamides. ... 

Ketene 8 reacts with ethoxy acetylene to give 9 [3] and phenyl methyl ketene 10 reacts with Z-alkene 11 to give 12 [4]. 

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