Sesterterpenes. 1. Stereospecific construction of the ceroplastol and ophiobolin ring systems via a common bicyclic intermediate

Boeckman, Robert K.; Bershas, James P.; Clardy, Jon; Solheim, Barbara A.

doi:10.1021/jo00442a043

Cited by 27 publications

(13 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The pooled solutions from the kinetic runs showed a single peak on HPLC. After evaporation to a small volume and flash chromatography on silica gel with 5:1 hexane:acetone as eluant, the product, a colorless oil, was placed in an ampule and pumped free of solvent at 10~3 mm: NMR (CC14) 6.9 (s, 1 H, moves on dilution), 5.1-5.9 (m, 4 ), 4.1 (interlaced q, J = 7 Hz, 4 H), 2.5 (m, 1 ), 1.8 (s, 3 ), 1.23 (interlaced t, J = 7 Hz, 6 ), 1.15 (d, J = 8 Hz, 3 H); IR (CC14) 3300, 3020 (sh), 2980, 2930, 2880,1760, 1710 cm"1. Anal.…”

Section: Methodsmentioning

confidence: 99%

“…The latter does not quench the fluorescent indicator on the plate and fractions must be monitored by HPLC. Evaporation of pure fractions of 20 at 10"3 mm yielded 120 mg of colorless oil that was almost solid: NMR (CDC13) 7.25 (m, 1 H), 6.5 (d of m, 1 H), 5.5 (m, 2 ), 4.1 (m, 8 H), 2.6 (m, 2 ), 1.70 and 1.75 (overlapping s and d, 6 ), 1.35 (s, 3 H) overlapped by 1.28,1.25,1.22 (three interlaced t, 12 H) [the signals at 7.25 and 6.4 move upon dilution]; IR (CC14) 3350, 3020 (sh), 2980, 2910, 2870, 1750, 1710 cm"1; n25D 1 N, 11.34. The impure mixture of 18 and 19 was concentrated and reapplied to the Chromatotron.…”

Section: Methodsmentioning

confidence: 99%

“…From the predominance of 20 and the pattern of rate constants discussed below, the major initial product of 6 and DAZD (and precursor to 20) is the ene adduct 21. This would be expected to have greater reactivity toward DAZD than does 6 (or 22) but might be detectible if an overwhelming excess of 6 were present.…”

Section: / /mentioning

confidence: 99%

“…Sequential passage through two different preparative VPC columns was necessary before material pure enough (>99.8%) for either product or kinetic studies was obtained. Ironically, although 6 cannot give a Diels-Alder…”

mentioning

confidence: 99%

See 3 more Smart Citations

Ene reactions of conjugated dienes. 2. Dependence of rate on degree of hydrogen removed and s-cis or s-trans diene character

Jacobson¹,

Arvanitis²,

Eliasen³

et al. 1985

J. Org. Chem.

View full text Add to dashboard Cite

was treated with 0.1 M CH3C02H. When analyzed by IR after 50 min, the C=0 band of CH3C02H (1710 cm"1) was absent and the solution was water-white. After an additional 10 min, a white precipitate (Ph2BOCOCH3) formed. Two equivalents of MeOH (0.2 M) were added and the mixture was shaken. The white solid quickly dissolved. IR analysis of the resulting solution revealed a strong band at 1710 cm"1 (CH3C02H) and a new strong band at 1325 cm"1 assigned to Ph2BOMe. Proof that the white precipitate was the mixed anhydride, and not simply a TPB(MeOH) complex, was obtained by isolation of the white precipitate obtained in the reaction of 0.050 g of TPB (0.2 M) with 11.4 gL (0.2 M) of CH3C02H in 1 cc of CC14. The KBr IR spectrum of the precipitate showed a weak broad band at 1720 cm"1, assigned to the C=0 group of Ph2BOCOCH3. The solvent was vacuum stripped and was analyzed by IR which showed peaks assigned to benzene (1475,1805, 1950, 3015, and 3040 cm"1), in addition to peaks from CC14 and a trace of CH3C02H. The assignment of the structure Ph2BOCOCH3 for the white precipitate was also confirmed by NMR analysis. The aromatic protons ( 7.75) and CH3 protons ( 2.2) gave an integral ratio 3.9/1 (theoretical 3.3). Finally, elemental analysis of the solid gave results more in agreement with the assigned mixed anhydride structure rather than a simple TPB(CH3C02H) complex. Anal. Caled for

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: / /mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Ene reactions of conjugated dienes. 2. Dependence of rate on degree of hydrogen removed and s-cis or s-trans diene character

Jacobson¹,

Arvanitis²,

Eliasen³

et al. 1985

J. Org. Chem.

View full text Add to dashboard Cite

show abstract

“…Regioselective cyclization of (118) via the ketone enolate occurs to give (119).120 Zinc is necessary for a reasonable yield, and longer heating rearranges (119) to (120). Similarly, but under standard conditions, the 4-ketopyran (121) cyclizes regioselectively to (122) 88 and the anthraquinone (123) …”

Section: (Il') Anthracycline Antibioticsmentioning

confidence: 99%

Acylation of Esters, Ketones and Nitriles

Davis

Garratt

1991

Comprehensive Organic Synthesis

View full text Add to dashboard Cite

Reductions by Metal Alkoxyaluminum Hydrides

Málek

1985

Organic Reactions

View full text Add to dashboard Cite

Since the discovery of the reducing properties of diborane (1939), alkali metal borohydrides (1943), and alkali metal aluminohydrides (1946) by H. I. Schlesinger, H. C. Brown, W. G. Brown, and co‐workers, considerable effort has been expended to enhance the versatility and selectivity of these widely used hydride reagents. Whereas diborane exhibits medium reaction large differences exist between sodium borohydride and lithium aluminum hydride. In contrast to the reducing action of sodium borohydride, limited originally to aldehydes, ketones, and acid chlorides, lithium aluminum hydride readily attacks almost all reducible groups. The first progress in bridging this gap in reactivity can be traced to the availability of reagents that are easily prepared by addition of Lewis acids such as boron and aluminum halides to sodium borohydride and lithium aluminum hydride; in this manner diborane, chloroaluminum hydrides, and aluminum hydride have been made accessible as reducing agents. Parallel development led to sodium alkoxyborohydrides with generally higher reactivity than the parent hydride and to alkoxyaluminum hydrides, with markedly lower reactivity and increased chemoselectivity. On the other hand, the reducing capability of sodium borohydride and lithium aluminum hydride has been enhanced by the use of metal salt–hydride systems. A large number of other complex metal hydrides have gained importance as selective reducing agents: lithium aluminum hydride–nitrogen base complexes, sodium cyanoborohydride, lithium cyanoborohydride, sulfurated sodium borohydride, zinc borohydride, diisobutylaluminum hydride, alkylaluminum compounds such as triisobutylaluminum, and tri‐ n ‐butyltin hydride. Sterically hindered organoboranes such as lithium tri‐ sec ‐butylborohydride (L‐Selectride) exhibit excellent selectivity in reduction reactions. High asymmetric induction can be achieved with some chiral organoboranes. Lithium triethylborohydride (Super‐Hydride) is a selective and exceptionally powerful reducing agent. These complex metal hydrides often provide better regio‐ and stereoselectivities than those achieved with alkoxy‐substituted hydrides; nevertheless, the alkoxyhydrides are readily available and continue to be widely used as reducing agents. The purpose of this chapter is to present a critical review of reductions of the following compounds by metal alkoxyaluminum hydrides, alkoxyaluminum hydrides, and chiral metal alkoxyaluminohydride complexes: hydrocarbons, peroxides, ozonides, halogen compounds, unsaturated alcohols, aromatic alcohols, ethers, 1,2‐oxides, aldehydes, ketones, quinones, acetals, and ketals. The literature is covered through December 1981. Important papers that appeared through September 1982 are also reviewed. Some reactions relating to other than reducing properties of these hydrides are included for completeness. The emphasis is on the scope, limitations, and synthetic utility of the hydrides in reduction reactions and on the optimum conditions for their application as reducing agents. Currently accepted views of reaction mechanisms are discussed. Comparisons with reductions by other complex metal hydrides are limited to the most important transformations of the functional groups.

show abstract

Sesterterpenes. 1. Stereospecific construction of the ceroplastol and ophiobolin ring systems via a common bicyclic intermediate

Cited by 27 publications

References 4 publications

Ene reactions of conjugated dienes. 2. Dependence of rate on degree of hydrogen removed and s-cis or s-trans diene character

Ene reactions of conjugated dienes. 2. Dependence of rate on degree of hydrogen removed and s-cis or s-trans diene character

Acylation of Esters, Ketones and Nitriles

Reductions by Metal Alkoxyaluminum Hydrides

Contact Info

Product

Resources

About