Enantioselective Construction of Indanones from Cyclobutanols Using a Rhodium-Catalyzed C-C/C-H/C-C Bond Activation Process

Abstract

Enantioselective rhodium(I)-catalyzed reactions of tert-cyclobutanols lead via consecutive C-C/C-H/C-C bond activations to indanones with quaternary stereogenic centers.

Key words

rhodium - ring opening - quaternary stereogenic center - C-C activation - C-H activation

References and Notes

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10

Typical Procedure for the Preparation of ( S )-3-[( tert -Butyldimethylsilyloxy)methyl]-6-chloro-3-methylindan-1-one (6c) tert-Cyclobutanol trans- 1c (40.9 mg, 0.100 mmol), [Rh(cod)(OH)]₂ (1.14 mg, 2.50 µmol), (R)-Difluorphos (L3, 4.10 mg, 6.00 µmol), and Cs₂CO₃ (0.150 mmol, 48.9 mg) were weighted into an oven-dried vial equipped with a magnetic stir bar, capped with a septum, and purged with nitrogen. Dry xylenes (0.5 mL) were added, and the mixture was degassed with three freeze-pump-thaw cycles. The mixture was stirred for 10 min at 23 ˚C and subsequently immersed into a preheated oil bath (120 ˚C) for 12 h. After TLC analysis showed the complete conversion, the reaction mixture was cooled to 23 ˚C and directly purified on silica gel (pentane-EtOAc 30:1, R _f = 0.18) giving 32.2 mg (99%, 93% ee) of indanone (S)- 6c as colorless oil. ^¹H NMR (400 MHz, CDCl₃): δ = 7.71-7.60 (m, 1 H), 7.54 (dd, J = 8.2, 2.1 Hz, 1 H), 7.45 (dd, J = 8.2, 0.5 Hz, 1 H), 3.62-3.56 (m, 2 H), 2.75 (d, J = 18.7 Hz, 1 H), 2.41 (d, J = 18.7 Hz, 1 H), 1.40 (s, 3 H), 0.77 (s, 9 H), -0.06 (s, 3 H), -0.13 (s, 3 H) ppm. ^¹³C NMR (100 MHz, CDCl₃): δ = 204.0, 158.2, 138.5, 134.3, 134.1, 125.7, 122.9, 70.7, 48.5, 44.1, 25.6, 23.4, 18.1, -5.7, -5.8. HRMS (EI⁺): m/z calcd for C₁₃H₁₆ClO₂Si [M - C₄H₉]⁺: 267.0603; found: 267.0603. IR (ATR): 2955, 2929, 2885, 2856, 1720, 1602, 1470, 1254, 1236, 1180, 1109, 837, 777 cm^-¹. [α]_D ^²0 -21 (c 0.94, CHCl₃).

11

The absolute configuration of compounds 6 were assigned in analogy to the reported cleavage site. See ref. 4c,d, and 6.