Stille Couplings Catalytic in Tin:  A “Sn−F” Approach

Abstract

A new tin recycling method for Stille couplings catalytic in tin is reported. PMHS made hypercoordinate by KF((aq)) allows Me(3)SnH to be efficiently recycled during a Pd(0)-catalyzed hydrostannation/Stille cascade. Relative to previously disclosed protocols, reaction times are shorter and because this process is believed to proceed through a Me(3)SnF intermediate the hazards and problems associated with trimethyltins are also diminished.[reaction: see text]

Recent advances in transition metal-free catalytic hydroelementation (E = B, Si, Ge, and Sn) of alkynes

“…159 The Maleczka group previously reported the in situ reduction of organotin halides to organotin hydrides involving an organotin oxide intermediate in the presence of aqueous Na 2 CO 3 and PMHS (polymethylhydrosiloxane). [160][161][162] Based on this and Yamamoto's protocol, 159 Maleczka et al developed a one-pot allylation-hydrostannation sequence for the reduction of alkynals, in which tin halide as the initial product was reduced to an organotin hydride, and this tin hydride was subsequently consumed for the hydrostannation of the alkyne unit on the allylated intermediate in the catalytic system of 2 0 /PMHS (Scheme 54). 163 Under the optimal conditions [(i) BF 3 $OEt 2 and allylstannes (1 equiv.…”

Hydrostannation of Alkynes

“…One of the noteworthy applications of the hydrostannation reactions lies in the selective generation of alkenylstannanes, which serve as vinyl anion synthetic equivalents as partners in Stille couplings,157,158 or by transformation into vinyl halides and further reaction with nucleophiles to afford stereodefined di-or trisubstituted olefins. 141,[159][160][161][162] Cascade hydrostannation /cyclization reactions for the synthesis of spirocyclic heterocycles have been also reported. 163,164 Hydrostannation reactions have also found frequent uses in natural product synthesis, with some selected examples described in general reviews.…”

Polymethylhydrosiloxane

“…201 This approach enables Stille couplings that are catalytic in tin. [203][204] PMHS has also been used in the Cu-catalyzed ring opening of a range of alkynyl epoxides to deliver hydroxyallenes, a small number of which are shown in eq 109. 205 This reaction was exploited in the total synthesis of (+)-varitriol and several analogs.…”