Reaction of ketenes withN,N-disubstituted α-aminomethyleneketones.XIX. Synthesis ofN,N-disubstituted 4-amino-3-phenyl-2H-furo[2,3-h]-1-benzopyran-2-ones (4-amino-3-phenylangelicins). Crystal and molecular structure of 3-Phenylangelicin

1,4-Cycloaddition of phenylchloroketene to N,N-disubstituted 5-aminomethylene-6,7-dihydrobenzo[b]- furan-4(5H)-ones gave the corresponding adducts, namely N,N-disubstituted 4-amino-3-chloro-3,4,5,6-tetra- hydro-3-phenyl-2H-furo[2,3-h]-l-benzopyran-2-ones II, which were dehydrochlorinated with DBN to N,N-disubstituted 4-amino-5,6-dihydro-3-phenyl-2H-furo[2,3-h]-1-benzopyran-2-ones III. Compounds III afforded the title compounds IV by dehydrogenation with DDQ. In the cycloaddition step, 3-phenylangelicin V, whose structure was confirmed by 1H-nmr shift reagents data and by X-ray crystal structure determination, was almost always formed, probably starting from II by dehydrochlorination, dehydrogenation and hydrogenolysis of the disubstituted amino group. Separation of V was achieved by alumina chromatography either in the cycloaddition step or, in most cases, in the dehydrochlorination step. 3-Phenylangelicin crystallizes in the trigonal system, space group R3, with cell parameters (hexagonal axes) a = b = 41.021(10), c = 3.888(2) A. The angelicin moiety forms a dihedral angle of 42.1(1)° with the phenyl substituent. Disordered solvent molecules of ethyl acetate are clathrated in channels in the direction of the crystallographic axis c.