Organic Letters
Letter
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(13) In the case of substrate 2j, the presence of DBU is essential for
the success of the (1 + 4) annulation reaction. Using P(NMe2)3 alone
led to the predominant formation of the reductive amination product
4b in 60% yield, and only trace amount of the annulation product 3r
(14) The Ts group on the nitrogen atom of pyrrolidine could be
deprotected by employing a known procedure with PhOH/HBr,
although the corresponding deprotecting product 6a was isolated in
(15) For basicity of three-coordinate phosphorus compounds, see:
̈
Bunten, K. A.; Moreno, C.; Poe, A. J. Dalton Trans. 2005, 1416.
(16) A phosphine-triggered general base catalysis and a sequential
nucleophilic addition-SN2 substitution for the cyclization of 4a are
also feasible in the case of P(NMe2)3. For phosphine-triggered general
base catalysis, see: Stewart, I. C.; Bergman, R. G.; Toste, F. D. J. Am.
Chem. Soc. 2003, 125, 8696.
(17) As for the δ-tosylamino enone 2 without a phenyl group such as
entries 17−19 in Table 2, the steric hindrance and the possible
interaction of the phenyl group with the keto/ester-carbonyl group in
intermediate C are believed to govern the stereochemical results.
E
Org. Lett. XXXX, XXX, XXX−XXX