Acyl zirconocenes

Scheme 1.34. Formation of acyl-zirconocene derivatives by carbonylation and their conversion into aldehydes, carboxylic acids, and derivatives thereof.

Insertion of carbon monoxide into Csp2—Zr bonds occurs readily at ambient temperatures or below to produce a,(5-unsaturated, reactive acyl zirconocene derivatives [27—29]. Early work by Schwartz demonstrated the potential of such intermediates in synthesis [5d], as they are highly susceptible to further conversions to a variety of carbonyl compounds depending upon manipulation. More recently, Huang has shown that HC1 converts 16 to an enal, that addition of a diaryl diselenide leads to selenoesters, and that exposure to a sulfenyl chloride gives thioesters (Scheme 4.11) [27,28]. All are obtained with (F)-stereochemistry, indicative of CO insertion with the expected retention of alkene geometry. 

Scheme 4.13. Conversion of an acyl zirconocene to a-hydroxy and a-amino ketones.

Scheme 4.14. Palladium-catalyzed couplings of acyl zirconocenes.

Scheme 4.16. Asymmetric 1,2-addition of acyl zirconocenes to cyclohexenone.

Figure 4.4. Proposed intermediate in Pd-catalyzed asymmetric 1,2-additions of acyl zirconocenes.

Scheme 4.17. Catalyst-dependent reactions of acyl zirconocenes with ynones.

Scheme 4.39. Copper-catalyzed alkylations of acyl zirconocenes.

Scheme 4.40. Regiochemistry associated with the prenylation of an acyl zirconocene.

Experimental procedure for acyl zirconocene generation and addition to imines [41] A... 

Butenolides,1 Addition of the Schwartz reagent to a protected propargylic alcohol (2) followed by carbonylation provides an acyl zirconocene complex (3). This is not isolated but treated in situ with iodine to provide an intermediate (a) that cyclizes to a 3,5-disubstituted butenolide (4). Optically active substrates undergo this sequence with no loss of optical purity. 

---