Improving the Atom Efficiency of the Wittig Reaction by a “Waste as Catalyst/Co‐catalyst” Strategy

Abstract

Waste not want not: Reported is a strategy to improve the atom economy of the Wittig reaction by using it in tandem reactions that directly employ the waste Ph3PO as an in‐situ‐generated Lewis base catalyst/co‐catalyst in the next step (see scheme).

Mass Efficiency of Alkene Syntheses with Tri- and Tetrasubstituted Double Bonds

“…The conventional bromination, using molecular bromine, produces slightly more waste than the hydrogen bromide/peroxide system. The catalytic Wittig-type reaction (entry 2b), which uses a silicon instead of a phosphorus compound, does not show an improvement compared to that of the classical Wittig reaction (entry 2a). The question is which coupled product can be recycled in a more environmentally friendly way.…”

“…The question is which coupled product can be recycled in a more environmentally friendly way. Attempts are regularly reported in the literature. , There does exist a commercial procedure for the classical variant of the Wittig reaction with triphenylphosphonium salts . The authors of the new method using a silicon compound argue for presenting an atom-efficient catalytic procedure but deliver no metrics.…”

Tandem One‐Pot Wittig/Reductive Aldol Reactions in which the Waste from One Process Catalyzes a Subsequent Reaction

“…However, Zhou and co-workers have very recently described a conceptual breakthrough in this context in which the byproduct of one reaction serves as the catalyst for the second reaction in one-pot reaction sequences. [2] Specifically they reported tandem Wittig-conjugate-reduction reaction cascades in which the Ph 3 PO generated as waste in the first process catalytically activates HSiCl 3 in the second step (Scheme 1 a). Furthermore, they also found that the Ph 3 PO formed in Wittig reactions could work together with a chiral salen alu-minium complex in catalytic asymmetric cyanosilylation reactions of enones formed in the first reaction (Scheme 1 b).…”

Metal‐Free Reductive Aldol Reactions

“…In this context, Zhou et al contributed a conceptually novel work where the byproduct of one reaction catalyzes the second reaction in a one-pot sequence. [30] In line with this concept, Toy and co-workers envisioned a tandem one-pot Wittig/reductive aldol sequence using the "waste as catalyst" strategy, Scheme 15. [31] It is known that the Wittig reaction generates an equivalent amount of phosphine oxide as the byproduct.…”