Ring opening diisobutylaluminum hydride

Resistance to reduction processes seems to be a general characteristic as most catalytic methods (as well as sodium in ethanol) reduce only the ring. However hydantoin can be reduced by diisobutylaluminum hydride to imidazolin-2-one (81TL2063), and imidazoline-2-thiones can be prepared from 2-thiohydantoins (70AHC(12)103). Oxidative procedures often result in ring opening (B-76MI4070i). 

Using nickel(O), generated from nickel(II) chloride with diisobutylaluminum hydride, as catalyst, cyanotrimethylsilane underwent addition to l-methylene-2-phenylcyclopropanes to give 2-phenyl-l-(trimethylsilylmethyl)cyclopropane-l-carbonitriIes 1 in poor yield. Palladium catalysis led to opening of the cyclopropane ring as the major process. 

There are many methods for the cleavage of 4,5-dihydrooxazoles once they have served their purpose. An effective method for hydrolyzing them back to carboxylic acids employs trifluoro-methanesulfonic anhydride <92SC13>. Intermediate ring-opened esters (100) are A(-methylated, then saponified to the acids (Scheme 34). The oxazoles may also be converted into aldehydes or nitriles. In a one-pot, two-step procedure, 4,5-dihydrooxazoles are transformed into alcohols (101) <93TIj4893>. Chloromethyl methyl ether converts the dihydrooxazoles into ring-opened amides in the first step, and these are reduced with diisobutylaluminum hydride (Scheme 35). 

A Wittig reaction of 1010 with allyltriphenylphosphonium bromide and potassium tert-butoxide produces a 4.3 1 mixture of ZjE dienes, the -diene being the desired isomer. Ring opening of the acetal with diisobutylaluminum hydride and subsequent photoisomerization of... 

In a preliminary paper by a Canadian team, it was reported that treatment of the known dehydrocordrastine with diisobutylaluminum hydride (Dibal) leads to equimolar amounts of the diastereomeric spirobenzylisoquinolines 18 and 19 in 76% yield. The reaction proceeds by reductive opening of the oxygen ring, and reclosure of the resulting enolate. ... 

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