Palladium-Catalyzed Conversion of β,γ-Unsaturated Silyl Sulfinates into (E)-Alkenes:  Asymmetric Synthesis of Polypropionate Fragments

Abstract

At low temperature, 1-alkoxy-1,3-dienes add to sulfur dioxide activated by a Lewis or protic acid generating zwitterionic intermediates that can be quenched by enoxysilanes. The resulting beta,gamma-unsaturated silyl sulfinates can be desilylated by 1:1 Pd(OAc)(2)/PPh(3) catalyst, liberating the corresponding beta,gamma-unsaturated sulfinic acids that undergo smooth and highly stereoselective retro-ene eliminations of sulfur dioxide. The method has been applied to generate enantiomerically pure polypropionate fragments.

Use of sultines in the asymmetric synthesis of polypropionate antibiotics

“…Although we have no proof for it, studies with trimethylsilyl 2-methylprop-2-enesulfinate have shown that Pd(OAc) 2 alone in MeCN does not catalyze the reaction. The presence of Ph 3 P and i-PrOH is crucial for success, and intermediacy of allyl-Pd species has been established [76]. The remarkable chirality transfer 26 to 27 strongly supports a mechanism in which Pd(0) adds oxidatively (retention of configuration) into the C-SO 2 SiMe 3 bond of 26 producing 33.…”

“…Subsequent desulfinylation into 34 and protolysis of the Pd-SiMe 3 bond giving i-PrOSiMe 3 (driving force) is expected to generate hydride 35 that undergoes regioselective and stereoselective β-insertion of hydride into the allyl-Pd intermediate. An alternative mechanism is to invoke that the Pd(0) catalyst role is just to promote the Si-sulfinate bond cleavage that generates the corresponding β,γ-unsaturated sulfinic acids that in turn undergo classical retro-ene elimination of SO 2 producing 27 [76]. Further studies are obviously necessary for a better view.…”

Expeditious Asymmetric Synthesis of a Stereoheptad Corresponding to the C(19)–C(27)‐Ansa Chain of Rifamycins: Formal Total Synthesis of Rifamycin S

“…For retro-ene desulfation of intermediates 20, recently developed conditions were applied successfully. [21] The use of previously described Et 3 NH + TfO À caused degradation, most probably because of b-elimination of the alkoxy group. 3-Acetoxydiene 5 f was slow to react and only 40 % of isomeric mixture was isolated together with unreacted starting material.…”

The Catalyzed Desulfinylative Allylation of Carbonyl Compounds with Alk‐2‐enesulfonyl Chlorides and Silyl Alk‐2‐enesulfinates

“…Preliminary studies within our group [31] have shown that silyl sulfinate 13 reacts with PdA C H T U N G T R E N N U N G (OAc) 2 /Ph 3 P to give allylpalladium complex 15 and Me 3 SiOAc (Scheme 6). Complex 15 was then converted, at 25 8C, into sulfone 16.…”