Table 1.

Phospha-Michael addition reactions of α,β-unsaturated ketones (4 or 5) with secondary phosphine oxides (6, 7, or 8)^a,b.

Entry	Substrate	Reaction time (min)	Temp (°C)	16α-isomer	16β-isomer	Yieldc (%)
1	4	60	100	9	10	87
2	4	90	100	13	14	90
3	4	60	130	17	18	92
4	5	60	125	11	12	91
5	5	90	125	15	16	89
6	5	60	140	19	20	87

^aReagents and conditions: α,β-unsaturated ketone (4 or 5, 1 equiv), secondary phosphine oxide (6, 7 or 8, 1 equiv), acetonitrile.

^bRatio (16α:16β = 2.3:1) obtained from the ¹H NMR spectrum of the crude diastereomeric mixture.

^cCombined yields of the two diastereomers obtained after flash chromatography.