Rearrangement with Dibal reduction

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

The key intermediate in the total synthesis of furaquinocin was obtained in good yield by a reductive Heck reaction that proceeded with a sterically hindered base pentamethylpiperidine (PMP) <02JA11616>. A new hypothesis for the major skeletal rearrangement (anthraquinone —> xanthone —> coumarin) that occurs in the complex biosynthesis of aflatoxin Bi was proposed. To test this hypothesis, an intermediate 11-hydroxy-O-methylstergmatocystin (HOMST) was synthesized as shown below. The key transformation in this synthesis involved the treatment of an ester-aldehyde with Pr3SiOTf, which smoothly produced a mixed acetal. Direct reduction with DIBAL-H led to the aldehyde. The desired product was eventually obtained via several steps as shown <02JA5294>. 

The open-chain tautomers 24b and 25 of precursor incipient imidazolidine and perhydropyrimidine derivatives, which bear a six carbon transferable fragment, on acid-catalyzed reactions with tryptamine formed the diester 85. A similar reaction of 24a leads to quantitative formation of 86 and the reaction of 25 with tryptamine is appreciably faster than that of 24b. Sodium cyanoborohydride/acetic acid reduction of 85 was accompanied by intramolecular aminolysis to form piperidone 87. Its Bischler-Napieralski cyclization followed by borohydride reduction gave cis- and trara-isomers of indoloquinolizine ester 88, which on hydrolysis to acid and subsequent methylene lactam rearrangement gave methylene lactam 89. Its DIBAL reduction gave 18- or-deplancheine 84a (88T6187). 

In conjuction with Triethylaluminum, DIBAL has been used to mediate a reductive pinacol rearrangement. with enantiocontrol,... 

Ireland and co-workers, in their synthesis of the prostanoid skeleton, have described the use of the ester enolate modification of the aliphatic Claisen rearrangement to produce the cyclopentane ring C-8—C-12 bond, viz. (74) ->(75). Conversion of the silyl ester (75) into the lactone (76), with a trace of acid, followed by reduction with DIBAL and aldol cyclization, then led to the prostanoid (77) (Scheme 20). 

Sharpless and Masumune have applied the AE reaction on chiral allylic alcohols to prepare all 8 of the L-hexoses. ° AE reaction on allylic alcohol 52 provides the epoxy alcohol 53 in 92% yield and in >95% ee. Base catalyze Payne rearrangement followed by ring opening with phenyl thiolate provides diol 54. Protection of the diol is followed by oxidation of the sulfide to the sulfoxide via m-CPBA, Pummerer rearrangement to give the gm-acetoxy sulfide intermediate and finally reduction using Dibal to yield the desired aldehyde 56. Homer-Emmons olefination followed by reduction sets up the second substrate for the AE reaction. The AE reaction on optically active 57 is reagent... 

Treatment of the amide 210 with diisobutylaluminium hydride (DIBAL-H) produces not only the expected reduction product 211 but also gives a mixture of the pyrrolonaphthyridine 212 and the indoloquinoline 213. Treatment of 212 with 50% acetic acid results in rearrangement to 213 (Equation 54) <1996JOC7882>. 

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