Quinone epoxides. Part III. Stereospecific reductions with metal hydrides

Abstract

Reduction of 1.4-naphthoquinone epoxide with sodium borohydride (1 equiv.) is shown to give the isomeric r-2.3-epoxy-3.4-dihydro-c-4-hydroxynaphthalen-I (2H)-one ( I I I a ) and r-2,3-epoxy-3,4-dihydro-t-4-hydroxynaphthalen-I (2H)-one ( I I I b ) in a ratio of ca. 11 : 1. With the same reagent juglone epoxide (5-hydroxy-I ,4naphthoquinone epoxide) is selectively and stereospecificalty reduced a t the chelated carbonyl to give r-2.3-epoxy-3,4-dihydro-c-4,5-dihydroxynaphthaten-l(2H) -one (IX) as the major product. The role of the chelating hydroxygroup is discussed. The configurations of the products are established on the basis of the n.m.r. spectra of the corresponding 2.3-epoxy-1.2.3.4-tetrahydronaphthalene-I ,4-diols. N.m.r. evidence also establishes the preferred conformations. THE structures of mycochrysone (I) 3 and cervicarcin (11) contain a 2,3-epoxy-4-hydroxynaphthalen-l(2H)one system [ e g . (111)], the two diastereoisomeric forms of which cannot be easily distinguished by chemical and physical methods4s5 We report the syntheses of compounds (IIIa and b) and describe the properties and stereochemistry of these and related compounds which are of particdar relevance to the stereochemistry of ring D in myochrysone. In this paper we shall refer to compounds such as (IIIa), in which the hydroxy-and Part IT, A. Rashid and G. Read, J . Chem. SOG.

Phaeofurans and Sorbicillin Analogues from a FungicolousPhaeoacremoniumSpecies (NRRL 32148)

“…In addition, observation of four pairs of signals with very similar 13 C NMR chemical shifts (Table 1) suggested a pseudo-symmetrical structure. The NMR shifts for two of the oxymethine units (δ C 55.9 and 55.5/δ H 3.40 and 3.38) were diagnostic for the presence of a 1,2-disubstituted epoxide.…”

“…7,8 Interestingly, the relative stereochemistry of phaeofuran A (1) was readily assigned on the basis of symmetry considerations. Of the three possible diastereomeric structures of phaeofuran A, two of them have H-4 and H-7 cis to each other, leading to a plane of symmetry that would give rise to an achiral molecule showing only three 1 H NMR methine signals and four 13 C NMR signals. Therefore, H-4 and H-7 must be trans to each other in phaeofuran A, thereby establishing the relative stereochemistry as shown in 1.…”

“…Molecular modeling calculations for 1 (Spartan '02; Wavefunction, Inc.) supported the concept that the value for the cis relationship should be larger, since the expected dihedral bond angle would be approximately 30°, while that for the trans relationship would be nearly 90°, but it has been noted that employment of Karplus-type calculations relating bond geometry to J-values in such instances can be equivocal. 13 Ultimately, the larger J-value was assigned to the cis relationship as shown in Table 1 on the basis of the these considerations and by analogy to the assignment made for 2 (see below), though this is not considered to be definitive. Phaeofuran B (2) was isolated as an oil, and its molecular formula was assigned as C 12 H 18 O 5 on the basis of HRESIMS, 1 H NMR (Table 1), 13 C NMR (Table 1), and DEPT spectral data.…”

“…13 Ultimately, the larger J-value was assigned to the cis relationship as shown in Table 1 on the basis of the these considerations and by analogy to the assignment made for 2 (see below), though this is not considered to be definitive. Phaeofuran B (2) was isolated as an oil, and its molecular formula was assigned as C 12 H 18 O 5 on the basis of HRESIMS, 1 H NMR (Table 1), 13 C NMR (Table 1), and DEPT spectral data. Analysis of the ID NMR spectra revealed the presence of one methyl, three sp 3 methylenes (one oxygenated), one tetrasubstituted olefin unit, and six oxygenated sp 2 methines.…”

“…Compounds 3-5 are close analogs of the known antibiotic sorbicillin (7), 19 and the structures of 4 and 5 were determined by comparison of NMR data with those for related known metabolites, including 3, which was identified by inspection of its NMR spectra and comparison of these data to literature values. 18 Compound 4 was obtained as a yellow solid, and its formula was assigned as C 14 H 16 O 3 by analysis of EIMS (M + at m/z 232), 1 H NMR, 13 C NMR, and DEPT data ( Table 3 Compound 5 was obtained as a white powder, and its formula was assigned as C 14 H 18 O 4 by analysis of EIMS (M + at m/z 250), 1 H NMR, 13 C NMR, and DEPT data (Table 3), and by comparison with data for another close analog which differs from 5 only by replacement of the hydroxymethylene unit with an aldehyde group. 18 Inspection of the 1 H NMR spectrum of 5 revealed the presence of a downfield oxymethylene proton signal at δ 4.61, a broad OH singlet at δ 2.02, and a side-chain containing only one olefin unit (at C-4 and C-5) instead of two as in 3, 4, and 7.…”