Rhodium-catalyzed enantioselective cyclizations of ﾎｳ-alkynylaldehydes with acyl phosphonates: ligand- and substituent-controlled C-P or C-H bond cleavage.
英文:
Rhodium-catalyzed enantioselective cyclizations of ﾎｳ-alkynylaldehydes with acyl phosphonates: ligand- and substituent-controlled C-P or C-H bond cleavage.
N-Propargyl 2-aminoacetaldehydes R1C竕｡CCH2NTsCH2CHO undergo cyclization with P-benzoylphosphonates ArCOP(O)(OR2)2 with either C-P- or C-H-bond cleavage, yielding 1-tosylpyrrolidines I and II, resp. (R1 = Me, Bu, Et, Ph; R2 = iPr, Et, Me; Ar = Ph, 2-MeC6H4, 4-ClC6H4, 4-FC6H4, 4-MeOC6H4, Me, Et, iPr), in dependence on catalyst and substrate. Cationic rhodium(I)/(R)-H8-BINAP or (R)-Segphos complexes catalyze the cycloaddn., the H8-BINAP favoring C-P-cleavage and formation of I with high yields and >99% ee and Segphos favoring C-H-bond cleavage with formation of II. The substituents of both ﾎｳ-alkynylaldehydes and acyl phosphonates also control the chemoselectivity of the cyclization. [on SciFinder(R)]
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