Regioselective access of alkylidendibenzo[c,f]oxocine framework via cyclocarbopalladation/cross-coupling cascade reactions and reductive Heck strategy

Palladium-catalyzed dual strategies of cascade cyclocarbopalladation/cross-coupling of alkynes and a reductive Heck reaction have been developed to construct dibenzo[c,f]oxocine frameworks with tri- and tetra-substituted exo-cyclic alkenes with high stereo- and regio-control. The success of this efficient methodology has been demonstrated by the synthesis of a number of dibenzoxocines in moderate to good yields and in sufficient quantities to support their further development.

12-benzylidene-7,12-dihydro-5H-dibenzo[c,f]oxocine (8a): The material obtained after workup was subjected to column chromatography on silica gel with petroleum ether/EtOAc (19:1) as eluent to deliver pure 8a. Off white solid, yield = 82%,

mp. 134-136 oC,

IR (KBr): 2861, 1623, 1602 cm-1 , 1H NMR (400 MHz, CDCl3): δH = 7.47 (d, 1H, J = 7.2 Hz), 7.19-7.34 (m, 5H), 7.05-7.15 (m, 5H), 6.94-6.96 (m, 2H), 6.64 (s, 1H), 4.87 (s, 2H), 4.75 (s, 2H).

13C NMR (100 MHz, CDCl3): δC = 144.6, 142.1, 138.3, 137.4, 136.9, 129.9, 129.1, 128.9, 128.6, 128.3, 128.1, 127.9, 127.4, 127.0, 126.7, 73.0, 70.3.

HRMS (ESI [M+Na]+ ): for C22H18O calcd 321.1255; found 321.1245.

///////Regioselective, alkylidendibenzo[c,f]oxocine, cyclocarbopalladation/cross-coupling cascade reactions, reductive Heck strategy