Lactones, reaction with Dibal

Baeyer-Villiger oxidation afforded the desired lactone 28 accompanied with hydro-xycarboxylic acid 29 as a byproduct. After removal of the acid 29, the lactone was reduced with DIBAL-H and employed in the Wittig reaction to form the PG structure 31 (Scheme 4). 

One application of lactone 140 as a chiral synthon may be found in the asymmetric synthesis of (+)-12b-epidevinylantirhine (143), a cleaved product of geissoschizol (Scheme 28) [62-63]. Treatment of 140 with tryptamine in hot toluene afforded 142, which cyclized to lactam 142 by mesylation and an Sn2 displacement. Hie Bischler-Napieralski reaction of 142, followed by reduction of the resulting iminium salt with NaBH4, produced stereoselectively, the indolo[2,3-a]quinolizine as a single isomer, which was further reduced with DIBAL to give (+)-12b-epidevinylantirhine (143). 

One of the most reactive 1,3-dicarbonyl compounds used in the domino-Knoevenagel-hetero-Diels-Alder reaction is N,N-dimethyl barbituric acid 2. It has been shown that the fairly stable products can easily been transformed into other compounds via a reduction of the urea moiety with DIBAL-H [20]. Thus, reaction of 30 with DIBAL-H at 78 °C led to 46, which can be hydrolyzed to give 47 (Scheme 5.9). In a similar way, 48 was transformed into 50 via 49 and 12 to 52 via 51. The obtained compounds containing a lactone and an amide moiety can again be further transformed using DIBAL-H followed by an elimination. In this way, dihydropyran 54 is obtained from 50 via 53 as one example. 

A similar result has been found for certain sterically hindered esters. This reaction is similar to 10-31, with OCOR as the leaving group. Other lactones have been opened to co-hydroxy amides with Dibal BnNH2. ... 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

The syntheses of L-nogalose - and L-vinelose" - from L-rhamnose have been described. Catalytic osmylation of a,f) unsaturated esters (26) and (27), followed by hydrolysis or hydrogenolysis, has produced the branched-chain lactones (28) and (29), respectively. " A racemic synthesis of some branched-chain lactones started with an unusual reaction of some oxetanes. For example, compound (30), when treated with DIBAL, afforded the... 

The boron trifluoride-induced aldol reaction between isopropylidene-D-glyceraldehyde and 2-(trimethylsilyloxy)furan followed by treatment with trimethylsilyl chloride and dimethylcopper lithium gave lactone 52. This compound was converted into 2,3-dideoxy-3-C-methyl-D-i anno-heptose by treatment with DIBAL then hydrochloric acid, and into 2,3-dideoxy-2,3-di-C-methyl-D-... 

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