Protonolysis and deuterolysis

Cleavage of Zr—C a bonds occurs readily on treatment with H20 or dilute acids, while the Zr—Cp bond usually survives mild protonolysis conditions. The use of D20 or DC1/D20 permits the replacement of Zr with D. Deuterolysis provides a generally reliable method for establishing the presence of Zr—C bonds. Protonolysis or deuterolysis of Zr—Csp bonds proceeds with retention of configuration [97]. In the hydrozirconation of terminal alkynes, deuterium can be introduced at any of the three positions in the vinyl group in a completely regio- and stereoselective manner, as shown in Scheme 1.18. Although relatively little is known about the mechanistic details, the experimental results appear to be consistent with concerted c-bond metathesis (Pattern 13) between C—Zr and H— X bonds. 

These trends were further confirmed through reactions of the foregoing chiral carbonate and phosphate derivatives with other electrophiles (Eqs. 9.32-9.34) [39]. For example, on protonolysis or deuterolysis, the allenyltitanium intermediate derived from the tertiary carbonate of Eq. 9.32 afforded an alkyne of 90% enantiopurity. Based on the configuration of this product and the assumption of a syn elimination to form the allenyltitanium, the protonolysis was suggested to take place by a syn SE2 pathway. In contrast, chlorination of this allenyltitanium intermediate follows an anti pathway (Eq. 9.33). 

The reaction of nBu2ZrCp2 with 2 equivalents of PhC CPh provides the novel bicyclic gem-dizirconium complex 140 [236] (Scheme 7.42). Protonolysis of complex 140 with 3 n HC1 gives bibenzyl in 88% yield, while its deuterolysis with D20 provides tetradeuterio-bibenzyl 141 with 92 % deuterium incorporation. The dual path nature (142 versus 140) of the reaction of Cp2Zr with alkynes is an important factor in designing Zr-promoted cyclizations of alkynes, enynes, and diynes. 

The Stille reaction of fluorovinyltin reagents offers the greatest synthetic flexibility, and reactions with alkanoyl (e.g., formation of 5 ), aryl (e.g., formation of 6 ), allyl and vinyl halides have been reported. Stereospecific destannylation reactions ofa-fluorovinyltin reagents include protonolysis, deuterolysis and iodination reactions. Electrophilic fluorination of the C —Sn bond has also been reported. 

However, the protonolysis of alkenylmercurials derived from the solvomercuration of alkynes is known as a method for preparing stereoisomerically pure alkenes. Acidic deuterolysis provides also a convenient route to labelled organic substrates. For instance, in a study on the regio- and stereo-selectivity of the acetoxymercuration of alkynes, protodemercuration with acetic acid of a 3 1 mixture of the vi-... 

Acidic deuterolysis and protonolysis have also been used for clarification of the placement of the mercury atoms after the mercuration step, in particular for pxjrphyrin derivatives. ... 

---