Cycloadditions of Oxacyclic Allenes and a Catalytic Asymmetric Entryway to Enantioenriched Cyclic Allenes

Abstract

Scheme 2. Catalytic asymmetric approach and cycloaddition results. dmdba = 3,5,3',5'-dimethoxydibenzylideneacetone, KHMDS = potassium bis(trimethylsilyl)amide. Comins' Reagent = N-(5-chloro-2-pyridyl)bis(trifluoromethanesulfonimide), THF = tetrahydrofuran, OTf = trifluoromethanesulfonate.

Rhodium-catalysed tetradehydro-Diels–Alder reactions of enediynes via a rhodium-stabilized cyclic allene

“…This intermediate is of particular interest given that cyclic allenes are emerging as powerful building blocks in modern synthesis and the new conceptual approach described here should lead to further developments in this eld. [32][33][34] Further work on generating and harnessing allenic-rhodium and rhodium-stabilized allene species in catalytic processes is currently underway.…”

Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds

“…Nonetheless, cyclic allene generation and trapping provided (+)- 134 in 81% ee, reflective of >99% stereoretention. 192 Collectively, these results demonstrate the feasibility of transferring stereochemical information from the silyl triflate to the cycloadduct through an axially chiral cyclic allene, while providing access to enantioenriched polycyclic products.…”

“… 171 , 172 Our laboratory devised the alternative approach shown in Figure 21 . 191 , 192 Silyl triflates 128 would be prepared with control of absolute stereochemistry and subjected to mild fluoride-based conditions. This could lead to the transmission of stereochemical information to cyclic allenes 129 , which in turn could undergo stereospecific trapping with 18 to yield cycloadducts 130 .…”

Allenes in Diels–Alder Cycloadditions

“…76 The generation of cyclic strained allene dienophiles has seen a resurgence of late, with the mild Kobayashi method (originally devised for 1,2-didehydrobenzyne formation 77 ) being extended to the generation of six-membered carbocyclic, 78 azacyclic 79 and oxacyclic allenes. 80 A representative example of a strain-driven Diels-Alder cycloaddition in-…”