DIBAL substituted

DIBAL, NiCl2(dppp), toluene, CH2CI2, THF, or ether, 80-97% yield. These conditions are chemoselective for simple alkyl and phenolic allyl ethers. More highly substituted allyl ethers are unreactive. 

Diisobutylaluminum hydride (DIBAL-H) can also be used for partial reduction of cyclic imides37. Although less convenient than sodium borohydride, an important synthetic aspect is the fact that in the reduction of asymmetrically substituted imides, diisobutylaluminum hydride and sodium borohydride may show opposite regioselectivity38,39. 

Scheme 10. Synthesis of the ds-donor-acceptor-substituted TEE 86 [ 100]. DIBAL-H diisobutylaluminum hydride, PCC pyridinium chlorochromate, LDA lithium diisopropylamide...

After protection, the a-hydroxy esters can be reduced by DIBAL-H into O-protected a-hydroxyaldehydes that are very useful synthetic intermediates (e.g., leukotrienes,7-9 ionophore antibiotics,10 insect pheremones,11 etc.). The secondary hydroxyl group of the a-hydroxy esters may also be substituted with inversion of configuration after activation as triflates of nosylates (p-nitrobenzenesulfonates) to give a-alkyl esters12 ora-amino esters.13... 

Substituted succinonitriles give 3-substituted pyrroles on reduction with DIBAL-H (84TL1659) via diimine intermediates which undergo cyclization and aromatization (Scheme 39). This reaction was used in the synthesis of unusual pyrroles (e.g. 119) which were used to prepare sterically shielded porphyrins (94AG(E)889). 

Recent efforts in the area of Friedel-Crafts alkylations have focused on the direct introduction of alkyl groups bearing functionalities, and on intramolecular alkylative cycliz-ations. The cyclization of the 2-substituted thiophene (55) to (56) has been achieved in 65% yield (80JOC3159). Similarly, the 3-substituted thiophene (57) has been cyclized to the isomeric (58). In both cases, detosylation of the product was achieved by treatment with diisobutylaluminum hydride (DIBAL). An elegant bis-cyclization of the diene (59) to the octahydrodibenzothiophene (60) has been reported (70CJC2587). 

Related to this reaction is the acid treatment of the (l-hydFoxymethylcyclohexadiene)tricarbonyliron (45), prepared via DIBAL-H reduction of ester (26) or borane reduction of the corresponding carboxylic acid, which leads to the 1-methylcyclohexadienyliron complex (46 equation 18).11 Using these methods, it is therefore possible to prepare a range of alkyl-substituted dienyl complexes having a defined substitution pattern. 

Similarly, the silicon-substituted precursor 187 was obtained by the reaction of 184 and trimethylsilylacetylene in 88% yield (Scheme 23) <1999CPB1108>. The enyne 187 was hydroaluminated with DIBAL-H, followed by bromination with NBS to give (Z,Z)-dibromide 188 and its (Z,/. )-stcreoisomer 189 in a ratio 10 1 in ca. 60% yield. The dibromide 188 containing small amount of isomer 189 was treated with a excess of /-butyllithium, followed by (PhSC lzS resulting in ring closure to form the 2-trimethylsilyl-l-benzothiepine 29g in 26% yield, presumably via the 1,6-dilithium intermediate 190. 

The DIBAL-H reduction of lactam 175 and subsequent etherification of the resulting A,0-hemiacetal with TMSOTf resulted in 176 (Scheme 35). It was further reacted with a variety of nucleophiles in the presence of Lewis acid to afford corresponding a-substituted azonines 177 in high yields <2002TL3165>. 

Unprecedented high ann-selectivities are obtained when E-substituted chiral allylic alcohols are treated with bis(iodomethyl)zinc and the dioxaborolane ligand (eq 8). In contrast, the ryn-isomer is obtained if the substrate is treated with the zinc reagent in the absence of the chiral ligand. The method complements that involving the direct reduction of cyclopropylketones with LiAlH4 or DIBAL-H. z... 

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