Microwave-Assisted Improved Regioselective Synthesis of 12H-Benzopyrano[3,2-c][1]benzopyran-5-ones by Radical Cyclisation

Table 1

Preparation of radical precursors 3(a–h).

Entry	Product (3)	R^1	R^2	R^3	R^4	MWI time (A)	% yield (A)	% yield (B)	mp°C (lit. [67] mp°C)
(1)	3a	H	H	H	H	6 min	74	80	143 (142)
(2)	3b	H	H	H	OCH3	4 min	76	82	122 (122)
(3)	3c	H	CH3	H	H	8 min	85	88	157 (158)
(4)	3d	H	CH3	H	OCH3	8 min	75	81	167 (168)
(5)	3e	CH3	H	CH3	H	7 min	70	78	164-165 (165)
(6)	3f	CH3	H	CH3	OCH3	7 min	82	84	170 (170)
(7)	3g	H	H	CH3	H	10 min	89	93	115 (116)
(8)	3h	H	H	CH3	OCH3	10 min	76	86	145 (144)