Table 2.

Phosphines 2–catalyzed [4 + 2] annulation of the α-methylallenoate 11^a

Entry	Catalyst	Conv (%)b	Ratioc,d(12:13)	Yield (%)e(12)	ee (%)f(12)
1	2a	56	10:1	23	20
2	2b	74	>50:l	9	29
3	2c	77	7.1:1	10	28
4	2d	70	1.9:1	11	41
5	2e	80	14.1:1	26	23
6	2f	47	>50:l	6	14

^aReaction conditions: 7 (1 equiv, 0.1 mmol), 11 (2 equiv), the phosphine 2 (30 mol%), 4-Å MS (10 mg), and CH₂Cl₂ (2 mL)

^bConversion was determined using mesitylene as an internal standard

^cDetermined from the ¹H NMR spectrum of the crude mixture

^d12 and 13 were obtained as a mixture; no pure 13 was isolated, but its structure was inferred according to our mechanistic proposal in Scheme 4

^eNMR yield (internal standard: mesitylene)

^fDetermined through chiral HPLC analysis; the absolution configuration was determined through comparison with the data of the known compound in ref. [19].