Key intermediate for the total

One of the carbazole-l,4-quinones, 3-methoxy-2-methylcarbazole-l,4-quinone (941), required for the total synthesis of carbazomycin G (269), was already used as a key intermediate for the total synthesis of carbazoquinocin C, and was obtained by the addition of aniline (839) to 2-methoxy-3-methyl-l,4-benzoquinone (939), followed by oxidative cyclization with catalytic amounts of palladium(II) acetate (545,645) (see Schemes 5.124 and 5.125). Similarly, in a two-pot operation, 4-meth-oxyaniline (984) was transformed to 3,6-dimethoxy-2-methylcarbazole-l,4-quinone... 

Methyl- 1,3-cyclopentanedione is a key intermediate for the total synthesis of steroids.2 A number of methods have been described for its preparation, among them the condensation of succinic acid with propionyl chloride,3 and that of succinic anhydride with 2-buten-2-ol acetate,4 both in the presence of aluminum chloride. It has also been obtained from 3-methylcyclopentane-1,2,4-trione by catalytic hydrogenation5 and Wolff-Kishner reduction 6 The base-promoted cyclization of 4-oxohexanoic acid ethyl ester and diethyl propionylsuccinate with tertiary alkoxides was first reported by Bucourt.7 The present cyclization process provides an experimentally simple route to 2-methyl-1,3-cyclopentanedione. Using the same procedure, 4-oxoheptanoic acid ethyl ester has been cyclized to give 2-ethyl-l,3-cyclopentanedione in 46% yield... 

Benzo[ ]furan-based diazobutenoates were used as a substrate to make a cyclopropane in 89% yield via a rhodium-catalyzed intramolecular process, as can be seen in Equation (74). Cyclopropane 88 was the key intermediate for the total synthesis of diazonamide A <20000L3521>. 

As depicted below, Swem oxidation and acid-catalyzed ring closure reactions were employed to construct fully functionalized benzo[fc]furan, a key intermediate for the total synthesis of natural product kendomycin <03OL4657>. 

The palladium-catalyzed carbonylative annulation of o-hydroxyphenylacetylene was employed to generate methyl benzo[h]furan-3-carboxylate, a key intermediate for the total synthesis of the natural product wedelolactone <03JOC8500>. 

Moderate asymmetric induction and low yields are observed when the compound 5, prepared from (A, )-hexadienal and (15,25)-pseudoephedrine, undergoes cycloaddition with the nitroso derivative 6. The major cycloadduct 7 is obtained together with minor amounts of diastereomers (d.r. 62 24 11 3) and after chromatography is isolated in 32% yield. Its configuration is first assigned by H NMR, and then by conversion into the known (+ )-(S)-2-methyl-l-(4-toluenesulfonyl)piperidine. Compound 7 is the key intermediate for the total synthesis of an amino allose derivative135. 

Enolates derived from 2-phenylselanyl esters react with various electrophiles such as alkyl halides and benzeneselenenyl halides [45]. The Michael addition of the enolate, formed from ferf-butyl 2-phenylselanyl propanoate, to (R)-5-n-octyl(5ff)furan-2-one and subsequent iodination afforded a key intermediate for the total synthesis of (-)-Avenaciolide [46] (Scheme 37). 

In the laboratory of D. Tanner, a novel method was developed for the stereoselective synthesis of ( )-tributylstannyl-a,P-unsaturated ketones in two steps from secondary propargylic alcohols. The first step was the highly regio- and stereoselective Pd-catalyzed hydrostannylation of the triple bond followed by a mild Ley oxidation. This method was utilized for the construction of a key intermediate for the total synthesis of zoanthamine. 

By the use of appropriate dialkylating agents, it is possible to spiroannulate cyclohex-2-enones at the 6-position via kinetic lithium dienolates. This method was used by Stork et alP to prepare the enone (67), a key intermediate for the total synthesis of ( )-3-vetivone (Scheme 32). In the cycloalkylation step the cross-conjugated dienolate presumably adopts a conformation with the S-methyl group quasiaxial to the ring to avoid A -strain and the new C—C bond is formed trans to this group. 

Burgess reagent was found to be the only effective dehydroxylation method during a key intermediate for the total synthesis of fredericamycin A (86-87).26 The dehydration protocol produced the alkene in quantitative yield. However, if compound 86 is exposed to Burgess reagent in refluxing benzene, no reaction occurs. 

We have demonstrated an alternate and more direct route, the lipase-catalyzed stereoselective acetylation of racemic 7-[AT,iV -bis(benzyloxycarbonyl) iV-(guanidinoheptan-oyl)]-a-hydroxyglycine 123 to the corresponding 5-(—)-acetate 124 and unreacted alcohol (+)-123 [218] 5-(—)-acetate 124 (Fig. 43) is a key intermediate for the total chemical... 

---