Table 2. Scope for Dehydrogenative Annulation^a.

entry	aldehydes 2	yield (%)b
	R2	3		4
1	Ph	3aa	50 (59)	4aa	10 (14)
2	4-OMe-C6H4	3ab	13 (21)	4ab	4 (7)
3	4-Me-C6H4	3ac	32 (38)	4ac	14 (20)
4	4-Cl-C6H4	3ad	50 (60)	4ad	13 (16)
5	4-CN-C6H4	3ae	63 (71)	4ae	(2)cd
6	4-NO2-C6H4	3af	51 (73)	4af	(3)cd
7	2-Me-C6H4	3ag	52 (57)	4ag	10 (12)
8	3-Me-C6H4	3ah	40 (46)	4ah	14 (18)
9	1-naphthyl	3ai	53 (64)	4ai	23 (25)
10	2-naphthyl	3aj	40 (47)	4aj	16 (24)
11	3-thienyl	3ak	12 (17)	4ak	(9)cd
12	n-Bu	3al	22 (24)	4al	e
13	sec-Bu	3am	31 (34)	4am	f
14	tert-Bu	3an	28 (30)	4an	15 (21)
15	cyclohexyl	3ao	26 (32)	4ao	f

^aReaction conditions: 1a (0.10 mmol), 2 (3.0 equiv), [Ph₃C]-[B(C₆F₅)₄] (1.1 equiv), and DTBMP (1.5 equiv).

^bIsolated yields based on 1a. NMR yields based on the internal standard Me₂Ph₂Si in parentheses.

^cNot isolated.

^dDetection by the proton signals for NMR spectrum relative to the authentic sample. See Experimental Section in detail.

^eNot obtained.

^fObtained silyl enol ether 5 instead of 4.