Synthesis stereospeeific

A series of optically active linear tetradentate ligands, which have been stereospeeifically synthesized, have been used to prepare complexes with a trans-[CoN Cl2] core and both five- and six-membered chelate rings, in an attempt to correlate the sign of the Cotton effect with the known chiralities of compounds. How ever, a complete correlation was not possible. The synthesis, resolution, and properties of some oxalato, malonato, and diacido complexes of Co " with the stereospecific flexible tetramine ligands 5-Me-3,2,3-tet and NA -bis-(2-picoyl)-l-methyl-1,2-diaminoethane (picpn) have been reported. The stereospecificity is demonstrated by comparison of the optical rotation of the ligand prepared via an asymmetric synthesis with that of the ligand isolated from a resolved complex. The stereochemistry of the complexes has been deduced. ... 

Stereospeeific synthesis of IJ-dieues. Corey el al. have described a new synthesis of 1,3-dienes based on the highly stereospeeific cis addition of alkylcopper reagents to a,p-acctylenic carbonyl compounds (3, 108). Thus the reaction of methyl 4-trimethyl-siloxy-2-nonynoate (I ) in THF with divinylcopperlithium (1.25 cq.) at - 90° and then at — 78° affords the pure madduct (2) in > 90% yield. Treatment of (2) with melhanolic hydrochloric acid effects cleavage of the trimethylsilyl ether and lactonization to give (3). 

Because borane additions to double bonds and subsequent oxidation are so selective, this sequence allows the stereospeeific and regioselective synthesis of alcohols from alkenes. The anti-Markovnikov legioselectivity of the hydroboration-oxidation sequence complements that of acid-catalyzed hydration and oxymercuration-demercuration. In addition, hydroboration, like oxymercuration, occurs without the participation of carbocations therefore, rearrangements are not observed. 

A Stereospeeific and Regioselective Alcohol Synthesis hy Hydroboration-Oxidation... 

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