A One‐Pot Synthesis of Pyranocoumarins Through Microwave‐Promoted Propargyl Claisen Rearrangement/Wittig Olefination

Abstract

The reaction between propargyl ethers of hydroxybenzaldehydes and the ylide ethyl (triphenylphosphoranylidene)acetate was carried out under microwave irradiation to regioselectively afford angular pyranocoumarins. The chromene and coumarin heterocyclic scaffolds were simultaneously formed in the same synthetic step without changing the reaction conditions. The natural products seselin, braylin, and dipetalolactone were among the products synthesized by this method.

8‐Prenylflavanones through Microwave Promoted Tandem Claisen Rearrangement/6‐endo‐trig Cyclization and Cross Metathesis

“…For the chemical synthesis of chromenes we [ 59 ] and others [ 60 ] have used a microwave promoted propargyl‐Claisen rearrangement, a transformation that starts from propargyl ethers and proceeds through allene intermediates. [ 61 ] To install the chromene part and the 8‐allyl substituent simultaneously in the microwave promoted tandem sequence, the chalcone 17 , bearing a propargyl and an allyl ether, was required as a starting material (Scheme 1).…”

“…[ 61 ] To install the chromene part and the 8‐allyl substituent simultaneously in the microwave promoted tandem sequence, the chalcone 17 , bearing a propargyl and an allyl ether, was required as a starting material (Scheme 1). This compound was synthesized in two steps from 15 [ 59 ] via O ‐allylation and subsequent Claisen‐Schmidt condensation of 16 and benzaldehyde. Submission of 17 to the optimized conditions for the microwave promoted Claisen‐rearrangement/6‐endo‐cyclization furnished a 1:1 mixture of the desired linear product 18 and its angular isomer 19 .…”

“…[55,56] Although 8 has only one actual prenyl substituent it is nevertheless a double prenylated flavonoid, because the chromene part is biosynthetically derived from an ortho-prenyl phenol through a cyclase catalyzed cyclization. [57,58] For the chemical synthesis of chromenes we [59] and others [60] have used a microwave promoted propargyl-Claisen rearrangement, a transformation that starts from propargyl ethers and proceeds through allene intermediates. [61] To install the chromene part and the 8-allyl substituent simultaneously in the microwave promoted tandem sequence, the chalcone 17, bearing a propargyl and an allyl ether, was required as a starting material (Scheme 1).…”

Diastereoselective Synthesis and Functionalization of tert‐Butylsulfinyl‐2‐(Chlorodiphenylmethyl)Pyrrolidine

“…The authors have cited additional references within the Supporting Information. [20][21][22][23][24][25][26][27]…”

Functionalized Benzofurans via Microwave‐Promoted Tandem Claisen‐Rearrangement/5‐endo‐dig Cyclization

“…Along these lines, straightforward syntheses of pyranocoumarins , prenylcoumarins , furanocoumarins , chroman‐4‐ones , and chromene‐4‐ones were developed and implemented in the total synthesis of several natural products. In the above‐mentioned examples, the cyclization step proceeds through a nucleophilic acyl substitution (for the synthesis of coumarins) or through an addition across an electronically biased C─C‐multiple bond (for the synthesis of chroman‐4‐ones and chromene‐4‐ones).…”