Vitamin A has been synthesized cleanly and selectively with essentially complete control of stereoand regiochemistry in four linear and six overall steps from p-ionone and (E)-3-methyl-2-penten-4-yn-l-01 via Pd-catalyzed cross coupling of an alkenylzinc with an alkenyl iodide; the use of other metals, such as Al, Zr, Mg, B, Cu, and Sn, being inferior to that of Zn. Synthesis of conjugated dienes via direct coupling of two alkenyl derivatives is an attractive synthetic strategy, Critically needed are those procedures that display high cross/home coupling ratios and high stereo-, regio-, and chemoselectivities.' A Pd-catalyzed procedure involving alkenylalanes' introduced for the first time in 1976 provided satisfactory results with respect to the requirements specitied above. Since then several related Pd-catalyzed procedures involving various metals, such as Zr,3 Zn4 Mg,5 B,6 Cu,' and Sn,' have been reported. The great majority of the results available at present, however, pertain to the synthesis of sterically less demanding and functionally simple diencs.' Consequently, critical studies of the scope and limitations including comparison of the reported procedures are still lacking. In this study, we chose vitamin A (la)'O as a critical test case for probing the scope and limitations of known representative procedures. Herein we present a highly selective synthesis of vitamin A summarized in Scheme 1, which appears to represent the first application of the Pd-catalyzed alkenyl-alkenyl coupling to the synthesis of retinoids, and the results of comparison of various known procedures for Pd-catalyzed alkenyl-alkenyl coupling. 1 (a: Z=H, b: Z=THP, c: Z=CPhs, d: Z=SiPh2Bu-t ) Scheme 1 i) 1. LDATHF, 2. CIPO(OEt),, 3. LDA(2.2 x). ii) 1. b&AI, ClzZrCp;,CHaC12, Ia.THF. iii) 1. DIBAH(Zx),hexane, 2. I2 ,THF. iv) CISiPhzBu-t, E13N, DMAP (l%), CH$&. v) 1. t-BuLi (2x) , 2. ZnBrp ,THF , 3. Pd(PPh& (4%) vi) n-BQNF , THF.