Stereoselective Synthesis of Stannyl Enones via Palladium-Catalyzed and Free Radical Hydrostannation of Alkynyl Ketones with Trineophyltin Hydride

Abstract

A study on the addition of trineophyltin hydride (1) to alkynones under free radical (AIBN and Et3B) and palladium-catalyzed [(PPh3)2PdCl2] conditions is reported. The results obtained indicate that the addition of 1 to eight ynones catalyzed by bis(triphenylphosphine)palladium(II) chloride led in all cases to addition products in very high yields (80-96%). These additions take place with excellent regio- and stereochemistry, leading to the alpha adducts as major products in seven out of the eight cases studied. Also the E adducts, resulting from a syn attack, were the only (seven cases) or the predominant (one case) products. The radical hydrostannations initiated by AIBN of ynones 2-5 with 1 led to addition products in good yields (60-88%); with the more hindered ketones 6 and 7-9 the yields obtained were lower. The radical additions initiated by triethylboron to ynones 2-6 follow a similar pattern but with lower yields; no addition products in the hydrostannation of ynones 7-9 were detected. The new acyl-substituted vinylstannanes, owing to their greater stability compared with that of their tributyl- and trimethylstannyl analogues, can be purified by column chromatography using neutral alumina (in all cases) or silica gel 60 (in most cases) as adsorbents. Full 1H, 13C, and 119Sn NMR data are given.

A Tribute to Prof. Julio César Podestá

“…Thus, we established that the reactions of organotin hydrides containing bulky organic ligands like neophyl, phenyldimethylsilylmethyl, (-)-menthyl, and tripticyl are slower than those carried out with the more common organotin hydrides (methyl, n-butyl, phenyl), and that the stereoselectivity achieved with the bulky hydrides is higher. [5][6][7][8][9][10] We also demonstrated that hydrostannation of alkynes with bulky organotin hydrides is not only more stereoselective but the useful vinylstannanes obtained are much more stable than those obtained with the common organotin hydrides and the separation of organotin byproducts is quantitative.…”

Synthesis and some stereoselective radical additions of bis[(phenyldimethylsilyl)methyl]tin dihydride

“…92; 126.20; 126.45; 127.66; 127.70; 127.73; 128.12; 128.65; 132.93; 133.33; 133.47; 133.51; 141.24 (22.8 Table 2 shows that the addition of hydride 6 to phenylethyne, naphthylethyne, methyl propiolate, diphenylethyne, and methyl 3-phenylpropiolate leads exclusively to the Zvinylstannanes resulting from an anti attack, typical of radical hydrostannations. 2f, 3,4 A remarkable fact is the formation of the Z-adducts as sole products in the additions of hydride 6 to phenylethyne, naphtylethyne, and diphenylethyne. In previous studies, we have shown that the addition of trineophyl-and tris[(phenyldimethylsilyl)methyl]tin hydrides to phenylethyne and diphenylethyne 2f,3 leads to the E-adducts as the sole products.…”

“…The organic layer was separated, and the aqueous was extracted three times with diethyl ether. The combined organic extracts were dried over anhydrous MgSO 4 . Removal of the solvent under reduced pressure gave 6 as a liquid (2.2 g, 5.4 mmol, 85% …”

Synthesis of dineophyltin dihydride and stereoselective hydrostannation of alkynes and (E)-trisubstituted alkenes

“…Thus, reactions involving trineophyltin hydride are slower but their yields are similar or higher than those carried out with the more common triorganotin hydrides (Me, n-Bu, Ph) [5,6]. Also, vinylstannanes with the trineophyltin moiety are more stable than their tri-n-butyltin analogs [7], and the stereoselectivity observed was in many cases substantially higher [8]. Moreover, we have also observed that the separation of the organotin residues resulting from these reactions was simpler [6d].…”