Anthracyclines. XIII The Synthesis of (+)-(4R,6R)- and (+)-(4S,6R)-6-Acetyl-6-(t-butyldimethylsilyloxy)-4-ethoxy-4-methoxy-5,6,7,8-tetrahydronaphthalen-1(4H)-one: New Chiral AB Synthons for the Synthesis of (—)-7-Deoxydaunomycinone

The title dienones have been prepared from (-)-(2R,1′S)-8-benzyloxy-2-(1′-hydroxyethyl)-5-methoxy-1,2,3,4-tetrahydronaphthalen-2-ol, by a series of reactions in which the selective cleavage of an aryl methyl ether in the presence of an aryl ethyl ether plays a key role. This 10- step sequence proceeds in an overall yield of 55%, and chiral integrity is preserved throughout.

Anthracyclines. XII. The preparation of (—)-(7R)-7-Acetyl-7-(t-butyldimethylsilyoxy-1(4H)-one and (+)-(6R)-6-Acetyl-6-(t-butyldimethylsilyloxy)- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalene-1(4H)-one: an Improved Route to Chiral AB Synthons for 7-Deoxydaunomycinone

The title dienones (2) and (5) were prepared from the chiral alcohols (7a) and (7b) respectively. These key starting materials were in turn available from the reduction of 3-acetyl-5-benzyloxy-8-methoxy-1,2- dihydronaphthalene (6a) and 3-acetyl-8-benzyloxy-5-methoxy-1,2- dihydronaphthalene (6b) with lithium aluminium hydride modified with (—)-N- methylephedrine and N- ethylaniline . Chiral phase high-pressure liquid chromatography was used to analyse the enantioselectivity of these reductions which were shown to yield variable results depending upon the origin of the reducing agent.

Pinching group stabilization. The synthesis and thermal isomerization of 10-Oxapentacyclo[6.3.2.13,6.01,8.02,7]tetradeca-4,12-diene

Sensitized irradiation (benzophenone, 0�, N2, pyrex filter, medium pressure Hg lamp) of dimethyl tricyclo[4.2.1.02,5]nona-3,7-diene-3,4-dicarboxylate (11) in (E)-1,2-dichloroethene yielded a mixture of 1 : 1 adducts (13) and (14) by site selective [2 π+2 π] cycloaddition at the cyclobutene π-bond. Reduction of the (Z)-dichloro isomer(13) with lithium aluminium hydride formed the related diol (16) which is the immediate precursor to the cyclic ether (18). Dechlorination of (18) with zinc in ethanol forms the title diene (19). Thermolysis of the polycyclic diester (20) affords the fragmentation products cyclopentadiene and dimethyl benzene-1,4-dicarboxylate. In contrast, the title compound (19) containing the cyclic ether ring was more stable and yielded the novel isomer (28) as the major product only upon flash vacuum pyrolysis at 560�(1.5 × 10-2 Torr). This difference in behaviour is attributed to a pinching group effect exerted by the cyclic ether present in (19).

Anthracyclines. XI. A short, site-specific synthesis of unsymmetrical 3-Acetyl-5,8-dialkoxy-1,2-dihydronaphthalenes; key precursors to daunomycinone AB-synthons

5,8-Dihydronaphthalene-1,4-diol, readily available from benzoquinone and buta-1,3-diene, is isomerized by heating with strong sodium hydroxide, and acetylated (Ac2O), in situ, to form 5,8-diacetoxy-1,2-dihydronaphthalene. Catalysed (AlCl3) addition of acetyl chloride followed by dehydrochlorination (LiCI/HCONMe2) yielded 5,8-diacetoxy-3-acetyl-1,2-dihydronaphthalene (11) in 82% overall yield. Base hydrolysis of (11), followed by methylation (Me2SO4) gives 3-acetyl-5,8-dimethoxy-1,2-dihydronaphthalene in 94% yield, the most direct route to this product so far described. More importantly, the diacetate (11) is selectively deacetylated at C5 (Cs2CO3 in tetrahydrofuran, or K2CO3 in Me2SO) to form the related phenol, alkylation of which produces the 5-alkoxy compound. Further hydrolysis followed by alkylation yields the unsymmetrically, but regiospecifically substituted, 3-acetyl-5,8-dialkoxy-1,2-dihydronaphthalenes. This method is specifically illustrated by the production of 3-acetyl-5-benzyloxy-8-methoxy-1,2-dihydronaphthalene which is formed in a short, cost effective synthesis in a moderate overall yield (25%) based upon benzoquinone as starting material;significantly, no chromatographic separations are required.

Anthracyclines. X. The enantiospecific synthesis of ( - )-(7R)-7-Acetyl-7-hydroxy- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalen-1(4H)-one; a type I chiral dienone for the synthesis of 7-Deoxydaunomycinone

8-Benzyloxy-5-methoxy-3,4-dihydronaphthalene-2-carboxylic acid (34) has been prepared by a four-step sequence from 5-methoxy-8-hydroxy-3,4-dihydronaphthalen-1(2H)-one. Condensation of the unsaturated acid (34) with ethyl (S)-prolinate in the presence of dicyclohexylcarbodiimide afforded the amide (35) which was enantioselectively cyclized to the bromo lactone (37). Debromination with tributyltin hydride and subsequent reaction of the lactone with methyllithium afforded (-)-(2R)-2-acetyl-8-benzyloxy-5-methoxy-1,2,3,4-tetrahydronaphthalen-2-ol. Removal of the benzyl ether by catalytic hydrogenation and oxidation of the resulting phenol with thallium(III) nitrate afforded the title chiral dienone.

A practical route to alcohols in the 7,7-Dimethylbenzonorbornene (9,9-Dimethyl-1,4-methanonaphthalene) series

The previously undescribed exo-and endo-7,7-dimethylbenzonorbornen-5-ols, can be prepared by the selective hydrogenolysis of the central unsubstituted bond in the corresponding spirocyclopropyl derivatives. Other examples of the reaction are also described.

The regiospecific synthesis of an anthraquinone based upon the elaboration of the adduct of 1-acetoxyisobenzofuran with p-benzoquinone monoacetal

1-Acetoxyisobenzofuran (4) reacts regiospecifically with 4,4-dimethoxycyclohexa-2,5-dienone (p-benzoquinone monoacetal) (6) to yield a single [4π+2π] cycloadduct with endo stereochemistry. Treatment of this adduct (7) with sodium methoxide formed 1,10-dihydroxy-4,4-dimethoxy-4a,10- dihydroanthracen-9(4H)-one (12), which was oxidized by the Corey-Fleet reagent to afford 1-hydroxy-4-methoxyanthracene-9,10-dione. This model reaction illustrates the potential of this approach to the regiospecific synthesis of anthraquinones. Attempts to introduce methoxy substituents into the anthraquinone by using 4- and 7-methoxy-1-acetoxyisobenzofuran, isobenzofurans described for the first time, were less successful. This limitation is discussed.

The regiospecific cycloaddition of 8,8-dimethylisobenzofulvene with isobenzofuran, 1-methylisobenzofuran and 1,3-dimethylisobenzofuran

The mixed 1 : 1 adduct formed upon reaction of isobenzofuran with 8,8-dimethylisobenzofulvene is shown to have structure (5) resulting from a [10 + 8] cycloaddition in which the isobenzofulvene serves as the 10 π reagent and the isobenzofuran as the 8 π reagent. The reaction occurs stereospecifically and forms exclusively the endo adduct. Lanthanide-induced shift spectroscopy, 13C n.m.r. and 1H n.m.r. spectroscopy, and deuterium-labelling techniques have been used to establish this structure. The structure of the adducts (24) and (26) derived from 1-methylisobenzofuran and 1,3-dimethylisobenzofuran, respectively, have also been established. A PMO treatment of this reaction correctly predicts the structure of these products including the regiochemistry of the product (24) formed from 1-methylisobenzofuran.

Isobenzofulvenes. VIII. The structure of the dimers derived from 8,8-dimethylisobenzofulvene. A PMO treatment of the perispecificity in this dimerization and related cycloadditions involving isobenzofulvenes

8,8-Dimethylisobenzofulvene, generated from the reaction of ll-isopropylidenetricyclo[6,2,1,02.7]- undeca-2,4,6,9-tetraene (23) and 3,6-di(pyridin-2-yl)-s-tetrazine, undergoes spontaneous dimerization to form a mixture of two isomers. This is shown to be a mixture of endo (33) and exo isomers (37) resulting from [π10s+π8s] cyclodimerization, with the former isomer predominating. 1H and 13C n.m.r. spectroscopy, in conjunction with lanthanide shift reagents and spin decoupling, was used, together with chemical degradation, to determine the structure and stereochemistry of these products. Chemical interconversion has placed these structures on a firm basis since the structure of the minor isomer has been determined by X-ray structure analysis. The constancy of this dimer ratio in solvents of widely differing polarity, and in the absence of solvent, supports an isopolar transition state which is typical of many concerted electrocyclic processes. A complete PMO treatment of all possible modes of isobenzofulvene dimerization is presented and the results of these calculations are discussed in terms of the observed peri- and stereospecificities. In a similar way, the PMO model is successfully employed to explain the relative efficiencies of various polyenophiles in trapping the isobenzofulvene nucleus.

An investigation of the reaction of dehydrogenating agents with a stable 8-Oxatricyclo[4,3,0,07,9]nona-2,4-diene and related Bicylo[4,2,0]octa-2,4-dienes as a potential route to isobenzofurans

Reaction of the 7,8-dichlorobicyclo[4,2,0]octa-2,4-diene (9) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone yields the benzocyclobutene (10). Extension of this technique to the related bicyclo[4,2,0]octa-2,4,7-trienes (21) and (23), or 8-oxatricyclo[4,3,0,07,9]nona-2,4-diene (6) was unsuccessful. Manganese dioxide was equally unrewarding while o-chloranil reacted with these olefins to yield benzodioxins in a [4+2] cycloaddition reaction.

The preparation of a stable 8-oxatricyclo[4,3,0,07,9]nona-2,4-diene and an evaluation of its potential as a source for the photochemical generation of oxiren

The synthesis of 2-methyl-3,4,5-triphenyl-8-oxatricyclo[4,3,0,07,9]nona-2,4-diene (14) is described, the first stable member of this ring system. Preparation of (14) was achieved by reacting dibenzyl diazenedicarboxylate with 2-methyl-3,4,5-triphenylbicyclo[4,2,0]octa-2,4,7-triene (29) to form the adduct (30a), which was selectively epoxidized at the cyclobutenyl double bond with 3-chloroperbenzoic to yield the epoxide (32a). Removal of the benzyl groups (H2/Pd) from the hydrazo bridge of (32a), followed by oxidation (red mercuric oxide or hydrogen peroxide) yielded the putative azo compound (33) which spontaneously lost dinitrogen, even at -78�, to yield (14) as a crystalline solid, m.p. 128�. While (14) has the potential to undergo 1,2-photoaromatization to yield oxiren (4a), this is not realized and ring-opening to the cyclic epoxide (34) is the major photochemical reaction observed under various ultraviolet irradiation conditions. Isomerization of (14) into (34) also occurs under thermal conditions. The 1H n.m.r, spectra of (14) as well as its trapping with dienophiles is discussed.

Preparation and trapping of 1-Acetoxyisobenzofuran. The structure of a novel phthalide formed in the attempted generation of 1-Acetoxyisobenzofuran in the presence of quinones

A new potential synthesis of anthraquinones based upon 1-acetoxyisobenzofuran (4) is reported. The key reaction used to generate isobenzofurans, namely the s-tetrazine reaction, proceeds smoothly in the presence of N-methylmaleimide to yield the expected adduct (16). In contrast, the reaction takes a different path in the presence of quinones to yield a novel phthalide (15). These reactions are considered to involve a non-concerted fragmentation of the intermediate dihydro-pyridazine (3) to yield the stabilized zwitterionic species (13). The zwitterion leads on to the phthalide (15) in a two step sequence involving the quinone as oxidant, while normal fragmentation is the sole reaction in the absence of oxidant. ��� The structure of 3-[3',6'-di(pyridin-2''-yl)pyridazin-4'- yl]isobenzofuran-1(3H)-one (15) has been determined by single crystal X-ray diffraction and refined by full-matrix least squares to a residual of 0.107 for 1389 'observed' reflections. Crystals are monoclinic, P21/c, a 8.271(2), b 19.183(4), c 11.814(2)Ǻ, β 110.0(1)β.

Site- and stereo-selectivity in the reaction of bicyclo[4,2,0]octa-2,4-dienes and related 2,4,7-trienes with 3-chloroperbenzoic acid: the formation ofacid-sensitive ene-epoxides and their conversion into 1,4-epoxides

Controlled site selective peroxidation of the bicyclo[4,2,0]octa-2,4,7-trienes (1a), (1b) or the related 2,4-diene (9) by means of 3-chloroperbenzoic acid in a basic two-phase medium allows the isolation of ene epoxides; these are especially sensitive to acid and rearrange to 1,4-oxides upon treatment with commercial (D)chloroform. Regular 3-chloroperbenzoic acid peroxidation conditions yield the 1,4-oxides directly. A carbonium mechanism is proposed to account for the interconversion of the initially formed 1,2-oxides into the more stable 1,4-oxides; the benzocyclobutene and methylene alcohols isolated in some cases are accommodated within this mechanism. Structure determinations draw heavily on 13C n.m.r. spectroscopy, especially to distinguish between epoxides and 1,4-oxides. The X-ray structure of a key 1,4-Coxide (11) is presented. The concept of the steric bulk of a π-cloud is discussed in terms of its role in controlling the stereoselectivity of the epoxidation reaction.

In vitro studies of the rabbit immune system. VII. The generation of rabbit anti-mouse cytotoxic T lymphocytes

Lymphocytes from normal or immunized rabbits generated cell-mediated cytotoxic activity (CML) after culture with mitomycin C-treated mouse stimulator cells for 4--7 days. CML activity was detected in short term (4--6 h) isotope-release assays using 51Cr-labeled tumor cells or mitogen stimulated blast cells as targets. Rabbit CML effectors could distinguish between different mouse strains including congenics differing only at H-2. It was previously shown that rabbit CML precursors and effectors expressed antigens recognized by a specific anti-T cell serum (ATS). The current results demonstrate that T-enriched fractions from nylon wool columns were enriched for CTL precursors and were sufficient to generate CML responses. These data were most consistent with the xenogeneic CML being mediated by rabbit cytotoxic T-lymphocytes (CTL) analogous to murine CTL. Rabbit lymphocytes also produced a strong mixed lymphocyte (MLC) response when tested in microculture with mouse stimulator cells. However, optimal CML and MLC responses did not occur in lymphocytes from the same organ sources or subpopulation. These data implied that CML activity could be generated with little, if any, proliferation necessary.

An improved synthesis of 6-Methoxyanthranilic acid

6-Methoxyanthranilic acid (1) is prepared in three steps from 2,6- dinitrobenzoic acid (6) in an overall yield of 46%.

A comparative study of Jones's, Collins's and Corey's reagents in the chromium(VI) oxidation of an epimeric pair of allylic alcohols in the benzo-fused Norbornen-5-ol series

A comparison has been made between a series of chromium(VI) oxidizing agents, as well as manganese dioxide, a bicyclic allylic secondary alcohol, the exo-ol (7), being the substrate. Jones's, Collins's and Corey's reagents gave, in each case, a mixture of products: the main reactions were epoxidation to yield (8) and (9), normal ketone formation (10), and ring-fragmentation to form the indanol (11) and the indanone (12). All reagents yielded substantial amounts of epoxide, which is rare for Collins's reagent, and unprecedented for Corey's reagent, and varying amounts (13-30 %) of ketone, while Jones's reagent alone gave significant ring-opened products. A dramatic change in product composition was observed with the epimeric endo-alcohol (13), where Jones's reagent (only one studied) yielded the related α,β,-unsaturated ketone (10) in essentially quantitative yield. A discussion of these results is presented in terms of the current understanding of the mechanism of chromium oxidations.

The preparation and acid-catalysed rearrangement of a spiro epoxy alcohol in the benzo-fused norbornene series

Epoxidation of 3-(1?-methylethylidene)-1,2,3,4-tetrahydro-1,4- methanonaphthalen-exo-2-ol (1) with meta-chloroperbenzoic acid formed exclusively the exo-epoxide (2). Acid-catalysed rearrangement of this spiro epoxy alcohol yielded two ring-expanded keto alcohols, exo-8- hydroxy-6,6-dimethyl-6,7,8,9-tetrahydro-5,9-methano-5H- benzocyclohepten-7-one (24) and exo-8-hydroxy-7,7-dimethyl-6,7,8,9- tetrahydro-5,9-methano-5H-benzocyclohepten-6-one (21), with the former predominating. Chemical and spectroscopic (including l.i.s.) methods were used to determine the structure of (21) and (24).

An improved synthesis of 2-(1,1-Dimethylprop-2-enyl)indole

The condensation of aniline with 1-bromo-3,3-dimethylpent-4-en-2-one yields 2-(1,1-dimethylprop-2-enyl)indole.