Expanding the Scope of Enantioselective FerroPHANE‐Promoted [3+2] Annulations with α,β‐Unsaturated Ketones

Abstract

The planar chiral 2-phospha[3]ferrocenophane I has been shown to be the first efficient nucleophilic organocatalyst for the enantioselective synthesis of cyclopentenylphosphonates, through [3+2] cyclizations between diethyl allenylphosphonate and alpha,beta-unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cyclizations of allenic esters with dibenzylideneacetone and analogous bis-enones, leading to functionalised cyclopentenes with either monocyclic or spirocyclic structures (ee 84-95 %). It has been shown that the residual enone functions in the resulting cyclopentenes can be involved in subsequent cyclization steps to afford unprecedented C(2)-symmetric bis-cyclopentenylketones. In order to provide insight into the behaviour of FerroPHANE I as a chiral catalyst in [3+2] cyclisations, the energetically most favoured isomers of the key phosphine-allene adduct have been calculated by DFT methods. Factors likely to control the chiral induction process are highlighted.

Recent Advances in Organocatalytic Methods for Asymmetric CC Bond Formation

“…In reactions with a,b-unsaturated ketones excellent results are observed (Scheme 93). [202] Besides phosphine catalyzed reactions of allenoates and arylidene malonitriles [203] as well as allenylphosphonates and unsaturated ketones [204] have been reported by Marinetti et al…”

“…Besides phosphine catalyzed reactions of allenoates and arylidene malonitriles203 as well as allenylphosphonates and unsaturated ketones204 have been reported by Marinetti et al.…”

Catalytic Enantioselective Cycloaddition with Chiral Lewis Bases

“…In [93]. The origin of enantioinduction was rationalised by considering transition state 202 (Scheme 50).…”

Enantioselective Construction of All‐Carbon Quaternary Stereogenic Centers by Using Phosphine Catalysis

“…In 2008, Marinetti and co‐workers reported a new class of chiral phosphines based on a planar chiral 2‐phospha[3]ferrocenophane scaffold ( P11 ) that effectively catalyzed the Lu [3+2] annulation of allenic esters 10 with indanone‐derived exocyclic enones 11 to yield spirocyclic structures that contained a quaternary center with moderate enantioselectivities (Scheme a) . With dienones 13 , the annulation reaction tolerated substrates that contained aryl groups of different electronic natures, and high enantioselectivities were obtained (Scheme b) . Interestingly, when annulation product 15 was reacted with allene 1 a at elevated temperature, a second [3+2] annulation occurred, thereby affording bis‐spirocyclic product 16 with excellent diastereoselectivity and >99 % ee .…”