Squarate ester cascade

Methanol-0-4 methyl nitrite, and dimethyl disulfide have been examined as potential chemical probes for distinguishing between alkoxides and enolates in the gas phase.171 Methanol-0-d proved to be unsuitable and methyl nitrite reacts too slowly in contrast, the reactive ambident behaviour of dimethyl disulfide results in elimination across the C—S bond on reaction with alkoxides ( hard bases ) and attack at sulfur by enolates ( soft bases ). This probe has been applied to investigation of the anionic oxy-Cope rearrangement. The dianionic oxy-Cope rearrangement is a key step in a squarate ester cascade involving stereoinduced introduction of two alkenyllithium reagents cis to each other.172... 

Paquette, L. A. Feng Geng, F. A highly abbreviated synthesis of pentalenene by means of the squarate ester cascade, Org. Lett. 2002, 4, 4547-4549. 

Paquette LA, Geng F. Applications of the squarate ester cascade to the expeditious synthesis of hypnophilin, coriolin, and ceratopicanol. J. Am. Chem. Soc. 2002 124 9199-9203. 

Paquette, L. A. Cascade rearrangements following twofold addition of alkenyl anions to squarate esters. Eur. J. Org. Chem. 1998, 1709-... 

The cascade rearrangements following double addition of alkenyl anions to the squarate ester was initiated by Paquette from the clue of Asensio s finding that twofold addition of organolithium (MeLi, PhLi, etc.) leads to the facile electrocyclic ring opening to 1,4-diketones [102]. This expedient method for construction of complex polycycles is achieved by a simple one-pot process... 

A transannular aldol reaction is also part of the squa-rate ester cascade applied by Paquette and co-workers in their expeditious 10-step synthesis of hypnophilin, an antibiotic metabolite isolated from cultures of the fungus Pleurotellus hypnophilus. Sequential 1,2-additions of a pair of vinyl lithium reagents to the squarate ester 54 led to intermediates (i.e., 56 and 58) by either trans- or... 

---