Transition‐Metal‐Catalyzed Cyclization of Alkynals via Oxametallacycle Intermediates

Abstract

The transition‐metal‐catalyzed cyclization of alkynals viaoxametallacycle intermediates is a useful method for thestereoselective synthesis of cyclic allylic alcohol derivatives. The reductive cyclization reactions are catalyzed by titanium and nickel complexes using organosilanes, organoboranes, and organozincs as reducing agents. The alkylative, arylative, and alkenylative cyclization reactions are catalyzed by nickel complexes using organozincs and alkenylzirconiums. On the other hand, the recently developed rhodium‐catalyzed reductive cyclization reactions of alkynals allow using dihydrogen as a reducing agent without the use of organometalloid and organometallic reagents. Furthermore, very recently, the rhodium‐catalyzed acylative cyclization reactions of alkynals were accomplished by using aldehydes and acyl phosphonates as acylating reagents. Importantly, the use of the rhodium catalysts realized the enantioselective cyclization reactions of alkynals with excellent levels of enantioselection.

Nickel‐Catalyzed Chemo‐, Regio‐ and Diastereoselective Bond Formation through Proximal CC Cleavage of Benzocyclobutenones

“…[34] An otherwise similar rationale might account for [4+ +2]-cycloadducts utilizing alkyne counterparts (Scheme 6). [35] In conclusion, we have described the first intermolecular catalytic bond formation by proximal C1ÀC2 cleavage of benzocyclobutenones without prior carbonyl activation or employing noble metals.This procedure is characterized by its exceptional mild conditions and exquisite chemo-, regio-and diastereoselectivity profile using non-precious Ni catalysts, allowing for the preparation of av ariety of otherwise inaccessible carbocyclic skeletons in as traightforward manner.T he asymmetric version and further investigations of other related transformations are currently underway in our laboratories.…”

Gas-Phase Intramolecular Cyclization of Argentinated N-Allylbenzamides

“…At present, NHCs are most commonly accessed by one of two different methods: ringclosing metathesis of dienes [2][3][4] or cyclization [5][6][7], attributable to their facile substrate construction and the relatively mild reaction conditions.…”

Nickel‐Catalyzed Chemo‐, Regio‐ and Diastereoselective Bond Formation through Proximal CC Cleavage of Benzocyclobutenones

“…[30,31] As ubsequent b-carbon elimination event from either III or in situ generated seven-membered metallacycle [32,33] might lead to the formation of putative p-allyl Ni II metallacycle (IV)t hat ultimately undergoes reductive elimination to form the corresponding benzofused eight-membered ring. [35] In conclusion, we have described the first intermolecular catalytic bond formation by proximal C1ÀC2 cleavage of benzocyclobutenones without prior carbonyl activation or employing noble metals.This procedure is characterized by its exceptional mild conditions and exquisite chemo-, regio-and diastereoselectivity profile using non-precious Ni catalysts, allowing for the preparation of av ariety of otherwise inaccessible carbocyclic skeletons in as traightforward manner.T he asymmetric version and further investigations of other related transformations are currently underway in our laboratories. [35] In conclusion, we have described the first intermolecular catalytic bond formation by proximal C1ÀC2 cleavage of benzocyclobutenones without prior carbonyl activation or employing noble metals.This procedure is characterized by its exceptional mild conditions and exquisite chemo-, regio-and diastereoselectivity profile using non-precious Ni catalysts, allowing for the preparation of av ariety of otherwise inaccessible carbocyclic skeletons in as traightforward manner.T he asymmetric version and further investigations of other related transformations are currently underway in our laboratories.…”