VARMA RAJENDER S ET AL: 'Reduction of .alpha.,.beta.-unsaturated nitroalkenes with borane and borohydrides. A convenient route to 3-nitro-, 3-hydroxylamino-, and 3-amino-2H-1-benzopyran derivatives', JOURNAL OF HETEROCYCLIC CHEMISTRY, WILEY-BLACKWELL PUBLISHING, INC, US, vol. 24, no. 3, 1 January 1987 (1987-01-01), pages 767 - 772, XP002409692, ISSN: 0022-152X, DOI: 10.1002/JHET.5570240343