Trivalent Phosphine-Catalyzed [4+1] Spiro-annulation Reaction Using Allenyl Imide and Methylene Cyclocompounds

Abstract

The trivalent phosphine-catalyzed [4+1] spiro-annulation reaction of allenyl imide and activated methylene cyclocompounds has been developed for the construction of various spiro-2-cyclopenten-1-ones. Oxindoles, 3-isochromanones, and 2-indanones are selected as 1C synthons to capture the in situ-generated bis-electrophilic α,β-unsaturated ketenyl phosphonium intermediate, affording the corresponding monospiro- and bispiro-cyclopentenones in good to excellent yields (≤91%) under mild conditions. The primary attempt at asymmetric catalysis using monophosphine (R)-SITCP provides promising enantioselectivity (45% ee). A plausible reaction mechanism is also proposed.

Enantioselective phosphine-catalyzed [6 + 1] annulations of α-allyl allenoates with 1,1-bisnucleophiles

“…8,9 In addition, another allene-derived 1,4-biseletrophile is also reported by Huang et al , who used β′′-oxazolidinyl-substituted allenyl imide as a C4 synthon, achieving [4 + 1] annulations via tandem β′′-addition and γ-addition. 10 On the basis of these two types of leaving group-containing allenes, various other types of annulations have been developed with different bisnucleophiles, generating 5- or 6-membered rings. 11 Furthermore, although both the δ-acetoxy-substituted allenoate developed by Tong and the γ-alkenyl allenoate developed by our group exhibited δ-addition and remote 1,7-addition reactivity, 12 the construction of medium-sized rings through the annulations of long-chained allene-derived remote biselectrophiles still remains an elusive challenge, 13 probably owing to unfavourable enthalpic and entropic effects in the synthesis of medium-sized rings, 14 as well as the limited availability of long-chained allene-derived biselectrophiles.…”