Scheme 2. Proposed mechanism for the transformation of 5 to 6 tropic 1.5-H shift in the five-membered ring and then coordinate the metal carbonyl fragment. This step also establishes the cis configuration of R and the complex fragment. Thus, whereas the chiral center 4-C and the planar chirality arise during the diastereoselective, metal-induced carbene annelation, the configuration of the stereocenter 3 a-C presumably results from a thermodynamically controlled enamine/imine tautornerization.['] The mechanism proposed in Scheme 2 is supported by a labeling study, which showed that deuterium introduced at the 3-position of the aryl substituent of 5 a is incorporated exclusively as frans 4-D in 6a.Metal-induced aminocarbene annelation thus offers a novel diastereoselective entry to arene-Cr(CO), complexes, which may be further functionalized in a controlled fashion by metalation and nucleophilic addition.['] E,xperimental Procedures 5-Amino-2-pentyne hydrochloride, 4a (0.70 g, 5.85 mmol), wdS added to a solution of pentacarbonyl[methoxy(l -methoxy-2-phenyl)carbene]chromium. 3 (1.65 g, 4.82 mmol), and 4 mL of triethylamine in 10 mL of dichloromethane at -78 "C. After 30 min, the solvent was removed under high vacuum. Column-chromatographic workup (0 "C, petroleum ether/dichloromethane 211) afforded 5 a as a yellow-brown oil (1.63 g, 86%. 'H NMR (300 MHz. CDCI,): 6 = 9.43 (s, hr, 1 H, NHj. 7.21 (m. 1 H, 5-Hary,j, 7.00 (m, 1 H.4-H4,,,).6.89(d.J = 8.3 Hz,IH,6-H.,,,),6.74(m,l H. 3-Hd,,,),3.82(s,3H, OCH,), 3 25 (m. 2H, NCH,), 2.39 (m, 2 H,=CCH,), 1.86 (t. J = 2.5 Hz, 3 H.