Phosphine-Mediated MBH-Type/Acyl Transfer/Wittig Sequence for Construction of Functionalized Furo[3,2-c]coumarins

Cu(ii)-Mediated aerobic oxidative synthesis of sulfonated chromeno[4,3-c]pyrazol-4(2H)-ones

“…Products were purified by flash chromatography on 200–300 mesh silica gels, SiO 2 . All salicylaldehyde substrates 1 were synthesized according to reports from Lin's group, 2 Yang's group 12 a or Wang's group 12 e except 1j (see ESI for detail, Schemes S1–S6†).…”

“…Recently, Lin's group developed a methodology that uses a PPh 3 -catalyzed cascade reaction and forged functionalized furo[3,2- c ]coumarins with alkynoates and benzoyl chloride (Scheme 1a). 2 In the terms of chromenopyridinone construction, two groups have independently developed methods with different strategies. Rubiales's group 3 (Scheme 1b), in 2002, utilized self-developed 2-azadiene, condensing aza-Wittig reagent with aldehydes/ketones, following intramolecular [4 + 2] aza-Diels–Alder ( I ) as well as RuCl 3 -catalyzed oxidation, which afforded chromenopyridinone II .…”

Phosphine‐Mediated Rauhut‐Currier‐Type/Acyl Transfer/Wittig Strategy for Synthesis of Spirocyclopenta[c]chromene‐Indolinones

“…Recently, we have reported a novel method for the diversity‐oriented synthesis of the spiropentadiene pyrazolones and 1 H ‐oxepino[2,3‐ c ]pyrazoles by a tandem phospha‐1,6‐addition of PBu 3 to doubly conjugated pyrazolones (Scheme 1a) [2a] . Very recently, we have also demonstrated a new method for the construction of functionalized furo[3,2‐ c ]coumarins from terminal alkynoates, PPh 3 , and acyl chlorides in the presence of a base (Scheme 1b) [6] . In continuation of our interest in the chemoselective phosphine‐mediated transformations, [7] we conceived that an appropriately positioned α,β‐unsaturated carbonyl functionality within the alkynoate substrates could provide the two different electrophilic sites for Michael addition, which would facilitate the sequence of prominent reactions and thus leads to a series of complex skeletons.…”

“…[2a] Very recently, we have also demonstrated a new method for the construction of functionalized furo [3,2-c] coumarins from terminal alkynoates, PPh 3 , and acyl chlorides in the presence of a base (Scheme 1b). [6] In continuation of our interest in the chemoselective phosphine-mediated transformations, [7] we conceived that an appropriately positioned α,β-unsaturated carbonyl functionality within the alkynoate substrates could provide the two different electrophilic sites for Michael addition, which would facilitate the sequence of prominent reactions and thus leads to a series of complex skeletons. The most challenging part for the construction of such skeletons is the double functionalization at terminal alkynoate to generate a crucial δacylated intermediate II via a chemoselective acyl transfer reaction upon in situ formation of sevenmembered betaine I. Herein we wish to report an unprecedented phosphine-mediated construction of spirocyclopenta[c]chromenones embedded with privileged motifs such as oxindoles, 1,3-indanediones, and pyrazolones via the RC-type/acyl transfer/Wittig strategy in a one-pot manner (Scheme 1c).…”

[3 + 2] vs. [4 + 1] Annulation: revisiting mechanism studies on the phosphine-catalysed domino sequence of alkynoates and activated methylenes

“…Second, a [4 + 1] annulation pathway also stands a chance to explain the phosphine-catalysed annulation of 2-formylphenyl alkynoates with activated methylene compounds (Scheme 1b). According to Lin's report and our previous works, 8 conjugate addition of PR 3 to alkynoate 1 followed by an intramolecular nucleophilic attack on the aldehyde moiety (MBH-type reaction) could generate the ylide intermediate F . The subsequent [1,5]-proton shift and dehydration of ylide F lead to the formation of the phosphonium H .…”