Arylglyoxals in synthesis of heterocyclic compounds.

Recent Progress of the Synthetic Studies of Biologically Active Marine Cyclic Peptides and Depsipeptides

2,3-Dichloro-5,6-dicyano-1,4-benzoquinone-catalyzed reactions employing MnO2 as a stoichiometric oxidant.

which show anti-angiogenic activity,but have different structuralproperties from the knownangiogenesis inhibitors. To facilitate elucidation of themechanism of action of epoxyquinols A and B, the develop-ment of a method for their totalsynthesis and derivatization ishighly desirable. Though structurally epoxyquinols A and Bhave a highly functionalized and complicated heptacyclic ringsystem containing 12 stereocenters, biosynthetically it isproposed they are formed by an unusualoxidative dimeriza-tion of the much simpler epoxycyclohexenone 3(Scheme 1).

Total synthesis of (+)-epoxyquinols A and B.

Total synthesis of proposed amphidinolide A via a highly selective ring-closing metathesis.

Oxidation of benzylic and allylic alcohols with chemical manganese dioxide smoothly proceeded under mild reaction conditions to give the corresponding aldehydes and ketones, respectively, in high yields. It is well-known that activated manganese dioxide (MnO2) is a useful reagent both for selective oxidation of benzylic and allylic alcohols to aldehydes and ketones, respectively, and for dehydrogenation of heterocycles to heteroaromatics. 1 Although several methods for preparation of activated MnO2 have been reported, 2 preparations are very tedious and sometimes the oxidation efficiency lacks reproducibility. Commercially available activated MnO 2 can also be used, but again its activity varies widely. We have already reported that chemical manganese dioxide (CMD), 3 produced for dry battery manufacture, can be efficiently used for oxidation of some allylic alcohols 4 and for dehydrogenation of heterocycles such as thiazolines, 5 2,3- dihydrofurans, 6 3-pyrrolines, 7 and 2-pyrrolines. 8 Further investigations along this line have revealed that CMD is widely applicable to the selective oxidation of benzylic and allylic alcohols 1 to aldehydes and ketones 2, respectively, as shown in Scheme 1.

http://www.sciencemadness.org/talk/files.php?pid=34476&aid=502

M. Yamauchi

Papers

Chemical Manganese Dioxide (CMD), an Efficient Activated Manganese Dioxide. Application to Oxidation of Benzylic and Allylic Alcohols

Chemical Manganese Dioxide (CMD), an Efficient Activated Manganese Dioxide. Application to Oxidation of Benzylic and Allylic Alcohols.

有用な活性二酸化マンガン,化学二酸化マンガン(cmd) ベンジル及びアリルアルコール類の酸化への応用