CrO₃/NHPI Adsorbed on Activated Clay: A New Supported Reagent for Allylic Selective Oxidation of Δ⁵-Sterols

Figures & data

Scheme 1 Allylic selective oxidation of compounds 1a–e to compounds 2a–e.

Scheme 2 Allylic selective oxidation of compound 1f with protected 3β-hydroxyl group to compound 2f.

Scheme 3 Allylic selective oxidation of compound 1g to compound 2a accompanied by cleavage of the acetal protecting group.

Table 1. Allylic oxidations with CrO₃/NHPI-activated clay

Substrate ^a	Product	^1H-NMR ^b δ (ppm)	^13C-NMR ^b δ (ppm)	IR ^c (cm^−1)	Mp (°C)	Yield ^d (%)
1a	2a	5.71 (s, 1H, H-6),	219.7 (C-17), 200.3	3477.9,	236–238	67
		3.66 (m, 1H, H-3),	(C-7), 165.7 (C-5),	1726.2,
		1.23 (s, 3H, H-19),	124.8 (C-6), 69.2 (C-3),	1655.4,
		0.88 (s, 3H, H-18).	16.5(C-19),12.8 (C-18).	1067.0.
1b	2b	5.63 (s, 1H, H-6),	209.9 (C-20), 201.6	3495.9,	200–201	54
		3.60 (m, 1H, H-3),	(C-7), 166.1 (C-5),	1707.9,
		2.07 (s, 3H, H-21),	125.7 (C-6), 70.2 (C-3),	1658.6,
		1.14 (s, 3H, H-19),	31.6 (C-21), 17.3	1070.0.
		0.59 (s, 3H, H-18).	(C-19), 13.2 (C-18).
1c	2c	5.69 (s, 1H, H-6),	202.6 (C-7), 167.2	3519.2,	162–166	52
		3.68 (m, 1H, H-3),	(C-5), 125.8 (C-6), 70.2	1663.7,
		1.23 (s, 3H, H-19),	(C-3), 22.8 (C-26), 22.6	1061.3.
		0.88 (d, 3H, H-21),	(C-27), 18.9 (C-21),
		0.85 (m, 6H, H-26,	17.3 (C-19), 12.0
		27), 0.68 (s, 3H, H-18).	(C-18).
1d	2d	5.72 (s, 1H, H-6),	203.0 (C-7), 166.0	3429.2,	149–154	40
		5.20 (dd, 1H, H-22),	(C-5), 139.0 (C-6),	1670.1,
		5.05 (dd, 1H, H-23),	130.5 (C-22), 127.0	1054.9.
		3.70 (m, 1H, H-3),	(C-23), 71.4 (C-3).
		1.17 (d, 3H, H-21),
		0.87 (d, 3H, H-26),
		0.85 (t, 3H, H-29),
		0.84 (d, 3H, H-27).
1e	2e	5.70 (s, 1H, H-6),	201.6 (C-7), 165.4	3506.8,	198–203	58
		4.47 (m, 1H, H-16),	(C-5), 125.9 (C-6),	1667.9,
		3.67 (m, 1H, H-3),	109.2 (C-22), 81.0	1066.0.
		1.22 (s, 3H, H-19),	(C-16), 70.4 (C-3), 66.8
		1.10 (d, 3H,H-27),	(C-26), 17.3 (C-19, 17.1
		0.80 (d, 3H, H-21),	(C-27), 16.4 (C-18),
		0.79 (s, 3H, H-18).	14.6 (C-21).
1f	2f	5.72 (s, 1H, H-6),	219.3 (C-17), 199.8	1734.9,	184–186	75
		4.69 (m, 1H, H-3),	(C-7), 169.3 (CO,	1670.4		60 ^e
		2.02 (s, 3H,	acetate), 163.9 (C-5),	1630.9,
		–O–CO–CH3), 1.21 (s,	125.5 (C-6), 71.0 (C-3),	1026.9
		3H, H-19), 0.86 (s,	19.6 (CH3, acetate), 16.4
		3H, H-18).	(C-19), 12.8 (C-18).
1g	2a					40