Hydroxy, dehydration synthesis

Methyl vinyl ketone can be produced by the reactions of acetone and formaldehyde to form 4-hydroxy-2-butanone, followed by dehydration to the product (267,268). Methyl vinyl ketone can also be produced by the Mannich reaction of acetone, formaldehyde, and diethylamine (269). Preparation via the oxidation of saturated alcohols or ketones such as 2-butanol and methyl ethyl ketone is also known (270), and older patents report the synthesis of methyl vinyl ketone by the hydration of vinylacetylene (271,272). 

The hydroxy lactams are postulated to be intermediates in transformations of enol lactones to ene lactams. This hypothesis was proved by synthesis. For example, treatment of N-methylhydrastine (98) with dilute ammonium hydroxide resulted in hydroxy lactam 148, which by the action of hydrochloric acid underwent dehydration to produce fumaridine (113) (5). Similarily, fumschleicherine (120) in reaction with trifluoroacetic acid gave fumaramine (111) 121). Narceine amide (149) was prepared from (Z)-narceine enol lactone (101) in likewise fashion 100,122) and dehydrated to narceine imide (116). A large number of N-alkylated narceine amides was synthesized from (Z)-narceine enol lactone (101) and primary amines by Czech investigators for... 

Dehydrativeglycosylation of 1-hydroxy donors with Ph2S0/Tf20 in conjunction with thioglycoside acceptors opens the way for sequential double glycosylation, one-pot procedures for trisaccharide synthesis, as exemplified by the efficient one-pot synthesis of the a-Gal epitope and a hyaluronan trisaccharide [566]. This study also shows the potential of selenoglycoside as acceptors in dehydrative glycosylation (Scheme 4.112). 

It was found that the simultaneous dehydration and saponification of the hydroxy ester 267 used for synthesis of the /1-carotene precursor, ketone Cis (270), was accompanied by a very facile allylic rearrangement which gave rise to the C15 acid (268) having, however, a different arrangement of double bonds than that in /J-ionone146,148. It was shown that treatment of acid 268 with the specially purified phosphorus trichloride results... 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

The first phase of our efforts was the unambiguous synthesis of each model substrate. PN and PX were already well characterized materials (1) While direct synthesis of the phenyl and carbomethoxy compounds from PN and/or PX was attempted, this approach was unsuccessful due to the sluggish reactivity of the norbornenyl double bonds in these molecules (2). A successful approach to CBN and (fiBN based on N-phenyl maleimide (NPMI) trapping of the respective thermodynamically favored 1-substituted cyclopentadienes is shown in Equation 1. Similarly, kinetic trapping of 2-phenyl cyclopentadiene, from the in situ dehydration of 3-hydroxy, 3-phenyl cyclopentene, gives a clean yield of (f)VN (Equation 2). The remaining phenyl isomer (VX) and the three other carbomethoxy isomers (CBX, CVN, CVX) were all obtained by the thermal isomerization chemistry described in the next section of this paper. They were each isolated in pure form by liquid chromatography We were unable to obtain any (f)BX or any of the 7-substituted isomers by any means. 

Ph, R = H) and acetic anhydride-triethylamine was initially thought to be anhydro-2,3-diphenyl-4-hydroxy-l,3-thiazolium hydroxide, CijHiiNOS (114, R = R = Ph, R = H), but later studies established that the product had the molecular formula C30H24N2O2 and the constitution 116. The synthesis of the meso-ionic l,3-thiazol-4-one (114, R = R = Ph, R = H), orange-yellow needles, m.p. 113°-115°, was successfully achieved by dehydration of the acid (115, R = R = Ph, R = H) using acetic anhydride-triethylamine for a few minutes at room temperature. The acids (115, R = NR2, R = Ph, R = H) and acid anhydrides similarly yield the corresponding meso-ionic l,3-thiazol-4-ones (114, R = NRj, R = Ph, R = H). Analogous polycylic meso-ionic l,3-thiazol-4-ones have also been prepared. ... 

In 1973 Cava et al. reported the synthesis of 4,6-dimethyl-l/f,3if-thieno[3,4-c]thiophene (142) and l,3,4,6-tetraphenylthieno[3,4-cl-thiophene (149) ° as well as data on some chemicaJ conversions of the latter and the dehydration of 4,6-dimethoxycarbonyl-l/f,3H-thieno-[3,4-c]thiophene sulfoxide. Thienothiophene (149) was also obtained (42%) by Potts and McKeough by condensation of anhydro-4-hydroxy-2,3,5-triphenylthiazolium hydroxide with dibenzoylacetylene followed by reaction of the product with P S,. 

Coriolin (689), a metabolite of the Basidiomycete Coriolus consors, has attracted widespread interest because of its unusual anti-tumor activity and highly functionalized triquinane structure. Accordingly, a number of syntheses of689 have appeared on the scene. One of the earliest, due to Tatsuta, et al., begins with epoxide 690, whose preparation had been earlier realized in connection with their work on hirsutine (see Scheme LXIII). Deoxygenation of 690, hydrolysis, and cis-hydroxy-lation provided keto triol 691 (Scheme LXXII) The derived acetonide was transformed via 692 into tetraol 693 which could be selectively acetylated and dehydrated on both flanks of the carbonyl group. Deacetylation of 694 followed by epoxidation completed the synthesis. 

The reaction of a-bromoacetals with trimethylsilylenolates catalyzed by titanium tetrachloride provides /3-alkoxy-y-bromoketones, which are useful furan precursors (Scheme 33) (75CL527). A new synthesis of acylfurans is exemplified by the formation of the 3-acetyl derivative (146) by heating the brdmoalkene (145) (78JOC4596). 2,2-Dimethyl-3(2//)-furanone (148) has been synthesized from 3-hydroxy-3-methylbutan-2-one treatment with sodium hydride and ethyl formate gave the hydroxymethylene derivative (147), which was cyclized and dehydrated to the furanone (148) with hydrochloric acid (Scheme 34) (71TL4891). O... 

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