Tetmhdvn Leers, Vol. 35, No. 27, pp. 46694672, 1994 Elseviu scimce La Printed in Chap Britain oo4&4039/94 s7.oo+o.00 Expandlng the Versatility of Schwartz’ Reagent: Hydrozirconation of Vinyllc and Acetylenic Acyl Silanes Bruce H. Lipshutz,* Craig Llndsley, and Ashok Bhandari Department of Chemistry University of Calitornla, Santa Barbara, CA 93106 Summsry. By virtue of a ttiisopropylsilyi acyl Mane confaftwd within a s&strafe undwgo~ng h@wkvnatio~ ChemOspeciWty can be reanzed favoriiw additiofl across the a/ken8 or alkyne, rather tftan wnpefithw 1,2-a#.Wftion of hydria, 0 the carbonyfpotin of the molecUe_ Hydrozirconation reactions of alkenes and aikynes are especially valuable processes in zyxwvutsrqponml tha t the addition of Cp&Zr(H)CI (i.e., ‘Schwartz* reagent’) to the carbon-carbon multiple bond is highly regio- and (for acetylenes) stereoselective. 1 Moreover, both alkyl and vinyl zirconocenes are highly prone toward transmetalations with various Cu(l) species (e.g., Cu(l) salts,* higher order cyanocuprates,s etc.), which result in reactive cuprate complexes capable of transferring the desired ligand to a variety of electrophiles. Since much of our work in this area of late relies on an initial hydrozirconation. we are particularly cognizant of the limitations associated with this powerful reagent, for these wouid necessarily establish minimum constraints on any subsequent chemistry envisioned to derive from an initial tirconocene intermediate. Those limitations identified include (1) competing 1 ,Padditions of hydride to aldehydeketone-containing alkenes/alkynes$ and (2) the facility with which carbonyl- containing substrates participate in intra- or intermolecular acid-base compiexation.sls which can completely inhibit any second-stage cuprate-assisted transmetalation (Scheme 1)s In order to circumvent these problems, we considered use of a group ‘G’ which not only prevents both (1) and (2) from occurring, but (3) adds considerable flexibilll as to the nature of the substituent which could be inserted In its place. We now report a solution to these issues based on the chemistry of acyl si1anes.s 3 - cl 1 must block Zr-H 1,2_addRion cl 2 mus! block carbonyl-Zr ccmplexattcn cl 3 G must be zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA a procursor to several other groups