Attenuol—structure, stereochemistry and synthesis

Joshi, B. S.; Viswanathan, N.; Balakrishnan, Venkatachalam; Gawad, D. H.; Ravindranath, K. R.

doi:10.1016/0040-4020(79)80031-9

Cited by 13 publications

(1 citation statement)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[la]; one substituent of la was a phenoxyl acetyl in which the Me signal appeared at 2.29, and the other was an alkyloxyl acetyl in which the Me signal appeared at 2.07 in the 'H-nmr spectrum. The presence of 3-alkyl phenol and phenyl moieties was proven OR, by comparison of the 'Hand 13C-nmr spectra with those of 3-(12'-phenyldodecyl)phenol [4] and 3-(10'-phenyldecyl)-phenol [5], which were isolated from the same plant. The location of the OH group along the chain was determined by mass fragmentation in which the base peak at mlz 107 indicated the presence of the phenylmethoxyl unit.…”

mentioning

confidence: 99%

Kneglomeratanol, Kneglomeratanones A and B, and Related Bioactive Compounds from Knema glomerata

Zeng¹,

Gu²,

Fang³

et al. 1994

J. Nat. Prod.

View full text Add to dashboard Cite

One new phenylalkyl phenol, kneglomeratanol [1], and two new acetophenones, kneglomeratanones A [2] and B [3], together with ten known compounds, 3-(12'-phenyldodecyl)-phenol [4], 3-(10'-phenyldecyl)-phenol [5], 5-pentadecylresorcinol [6], 5-(10'-phenyldecyl)-resorcinol [7], 5-(12'-phenyldodecyl)-resorcinol [8], 2,4-dihydroxy-6-(10'-phenyldecyl)-acetophenone [9], 2-hydroxy-6-(12'-phenyldodecyl)-benzoic acid [10], formononetin, biochanin A, and 8-O-methylretusin, have been isolated from the stem bark of Knema glomerata. Brine shrimp lethality was used for the activity-directed chromatographic fractionations. All of these compounds showed moderate but significant toxicities to three human tumor cell lines and inhibited the growth of crown gall tumors on discs of potato tubers.

show abstract

mentioning

confidence: 99%

Kneglomeratanol, Kneglomeratanones A and B, and Related Bioactive Compounds from Knema glomerata

Zeng¹,

Gu²,

Fang³

et al. 1994

J. Nat. Prod.

View full text Add to dashboard Cite

show abstract

The IntramolecularDiels–Alder Reaction

Ciganek

1984

Organic Reactions

108

View full text Add to dashboard Cite

The Diels–Alder reaction is one of the most useful reactions available to the synthetic organic chemist. It is thus surprising that the intramolecular version, in which both diene and dienophile are part of the same molecule, remained virtually unexplored for many years. Early examples were often the result of unexpected observations, and the many advantages of this reaction were recognized and put to use in the synthesis of complex polycyclic molecules only recently. In the intramolecular Diels–Alder reaction, two rings are formed in one step. In addition to the six‐membered ring formed by the [4 + 2]cycloaddition, the product contains a second ring, the size of which depends on the length of the chain connecting diene and dienophile. Of the two possible regiochemical modes of addition, that leading to the fused product usually predominates to the virtual exclusion of the bridged product. The Diels–Alder reaction proceeds through a highly ordered transition state that is reflected in large negative activation entropies. In the intramolecular version, some of the ordering has been accomplished in advance by making the two reacting functionalities part of the same molecule. This results in less negative activation entropies and increased reaction rates under often surprisingly mild conditions. On the other hand, by using forcing conditions one can sometimes carry out intramolecular Diels–Alder additions that would be doomed to failure in the intermolecular version. Lower reaction temperatures, together with the constraints imposed by the connecting chain, often result in pronounced regio‐ and stereoselectivity. Side reactions such as dimerization or polymerization can be avoided by using high dilution or low pressures in the gas phase. Examples where the bimolecular Diels–Alder reaction interferes with the intramolecular cyclization are rare. All of these features suggest that the intramolecular Diels–Alder reaction should be considered for any synthesis of a molecule containing a six‐membered ring fused to a second ring, especially if that ring is five‐ or six‐membered. Such a synthetic scheme may be made convergent by building up the diene and dienophile portions separately and connecting them just prior to the actual cyclization. Another potential use of the intramolecular Diels–Alder reaction that has not received much attention to date is as a supplement to the intermolecular Diels–Alder reaction in cases where the latter is unsuccessful or gives the wrong regio‐ or stereochemistry. By judicious choice of the connecting chain, the reaction may be made to proceed with the desired selectivity; this is followed by cleavage of the chain and conversion of the two ends to the desired functionalities. Once the feasibility of employing the intramolecular Diels–Alder reaction has been recognized, the main challenge often becomes the preparation of the substrate. A discussion of that aspect is beyond the scope of this chapter; however, by scanning the tables for the particular diene, dienophile, and chain one is interested in, and then referring to the original literature, it will often be possible to obtain some indications on how to proceed. An attempt has been made to cover the literature of the thermal intramolecular Diels–Alder reaction as completely as possible up to and including the year 1981. Many of the papers that appeared in 1982 and some from 1983 have also been included. More recent references are given in an addendum at the end of the tabular survey.

show abstract