PALLADIUM-CATALYZED CYCLIZATION OF 1-IODO-SUBSTITUTED 1,4-DIENE, 1,5-DIENE, AND 1,6-DIENE AS WELL AS OF 5-IODO-1,5-DIENES IN THE PRESENCE OF CARBON-MONOXIDE

A series of omega-alkene-containing alkenyl iodides were prepared via (a) various allyl-, homoallyl-, and higher omega-alkenylmetalation rea ctions of alkynes involving Zn, Al-Zr, Zn-Zr, and Cu, (b) trans-hydroa lumination and Cu-catalyzed trans-carbomagnesiation of propargyl alcoh ols, and (c) Zr-promoted alkyne-alkene coupling. Various factors affec ting three cyclic acylpalladation (Types I-III Ac-Pd) and three cyclic carbopalladation (Types I-III C-Pd) processes of the omega-alkene-con taining alkenyl iodides under the influence of CO and Pd-phosphine cat alysts have been delineated. In the presence of methanol or other alco hols at relatively high pressures (30-100 atm) of CO (Conditions IV), Type II Ac-Pd products containing five-membered ketones, such as 22, 2 6-28, 30, and 32, can be obtained generally in high yields. The order of rates of various carbonylative cyclization reactions producing five -membered rings is as follows: lactonization > Type II Ac-Pd reaction > C-enolate trapping with malonate anion. The preparation of six-membe red ketones via the Type II Ac-Pd process is less satisfactory. Attemp ts to prepare seven-membered ketones failed, and no attempts were made to obtain small ring ketones. In the absence of an external nucleophi le (Conditions I and II), alpha-alkylidenecyclopentanones can be obtai ned in high yields via the Type I Ac-Pd process in cases where the ome ga-alkenyl group is 1,2-disubstituted. Terminal vinyl-containing 1,4-p entadienyl iodides can give Type I Ac-Pd products, e.g., 31, 33, 35, 5 6-58, and 65, in moderate to good yields only with the stoichiometric amount of a Pd-phosphine complex. In sharp contrast, 1,5-hexadienyl io dides give predominantly Type III Ac-Pd products, e.g., 5, 60, 63, and 64, in moderate yields under comparable conditions. The Type III Ac-P d products can be cleanly converted to the corresponding Type II Ac-Pd products via alcoholysis. At 1 atm of CO in the presence of an alcoho l (Conditions III), noncarbonylative cyclic carbopalladation process ( Types I-III C-Pd) can be observed along with premature esterification. With terminal vinyl-containing alkenyl iodides, the cyclic Heck react ion (Type I C-Pd) is the dominant path. In cases where the omega-alken yl group is 1,1-disubstituted, however, the Type II C-Pd process can b e observed selectively using either i-PrOH as an external nucleophile or a mixture consisting of H2O, MeOH, and DMF (1:10:20). Collectively, the three Ac-Pd processes and the Type II C-Pd process in conjunction with novel and efficient methods for the preparation of the required omega-alkene-containing alkenyl iodides provide a potentially useful m ethodology for the preparation of five- and six-membered-ring compound s.