Total Synthesis of 19-Nordigitoxigenin, An Antiaroside Y Aglycon

The first total synthesis of 19-nordigitoxigenin, an aglycon of antiroside Y, has been achieved. The key steps of our synthesis are (i) construction of the 19-norsteroid ring system via a Mizoroki–Heck reaction between a bromoanisole corresponding to the A-ring and cyclic alkene incorporating the CD-rings, followed by a Friedel–Crafts-type cyclodehydration, and (ii) incorporation of the butenolide moiety at C17 via a silyl-tethered radical cyclization and subsequent ozone oxidation

A Synthetic Strategy for Saxitoxin Skeleton by a Cascade Bromocyclization: Total Synthesis of (+)-Decarbamoyl-α-saxitoxinol

A new synthetic strategy for the formation of the ABC tricyclic framework of saxitoxin was developed. The BC ring moiety, including a <i>spiro</i>-aminal structure, was first constructed stereoselectively by a newly designed cascade bromocyclization of a readily available internal alkyne bearing guanidine and urea. The A ring was then synthesized by a guanylation of a cyclic urea, easily prepared via the oxidative cleavage of the diol of the cascade product, followed by addition of cyanide. This strategy enables the concise stereocontrolled total synthesis of (+)-decarbamoyl-α-saxitoxinol, which is a naturally occurring saxitoxin analogue

Palladium-Catalyzed Cascade Wacker/Allylation Sequence with Allylic Alcohols Leading to Allylated Dihydropyrones

We describe a cascade Wacker/allylation sequence of β-hydroxy ynones by directly using simple allylic alcohols. This palladium­(II)-catalyzed reaction occurs under mild conditions (0 °C to room temperature) and provides a new and efficient synthetic method for the preparation of allylated dihydropyrones. The regiochemical outcomes are consistent with a reaction pathway that includes an insertion/β-OH elimination sequence to form the allylic moiety. A remarkable changeover from allyl to formylethyl products occurs under the simple action of LiBr

Synthetic Route to Oscillatoxin D and Its Analogues

<i>O</i>-Methyloscillatoxin D and its analogues were concisely synthesized by a bioinspired intramolecular Mukaiyama aldol reaction as a key step, which involves the construction of a novel spiro-ether moiety