Diketones monocyclic

The easier nucleophilic addition to 2-benzopyrylium salts, compared with monocyclic analogs, leads to loss of selectivity by the cation towards nucleophiles present in the mixture when they possess approximately equal nucleophilicity (NH3, H20, ROH). This forms stable adducts 109 (R = Aik), under these conditions, and labile pseudobases 109 (R = H) which undergo ring opening to diketones 29. The benzo[c ]annelation also plays its role in the easy formation of anhydrobases 119, which are stabilized by two aryl rings. 

Most syntheses make the side-chain alkene by an elimination reaction so the first disconnection is an FGI adding HX back into the alkene. The last C-C bond-forming operation in most syntheses is an intramolecular aldol reaction to make the enone so that can be disconnected next. It is the starting material for the aldol, a simple monocyclic diketone, which is usually made by a fragmentation reaction because this is a good way to set up the stereochemistry. 

Dihalides and 1,5-ditosylates have been used for the preparation of fully-saturated monocyclic 1,2-diazepines 165 (Scheme 83). 5-Halo-aldehydes and 5-halo-ketones react with a wide range of substituted hydrazines to give 4,5,6,7-tetrahydro-l,2-diazepines 166 <1976H(4)1509>. The reaction of 1,5-diketones with hydrazine has been much used as a source of 5,6-dihydro-4/7- 1,2-diazepines 167 . 

The two carbonyl groups of symmetrical diketones are distinguishable, with the carbonyl group undergoing reduction doing so with enantiotopic specificity. Some acyclic and monocyclic examples are shown in Scheme 9.- 2,44.49.50 Once more, enantiomeric products can be selected by the use of organisms with opposite enantiotopic face specificities, as shown for the reduction of (19) to (/ )- or (S)-(20) (Scheme 10). ... 

A possible biosynthesis of the structurally related Triphyophyllum alkaloids fits impressingly well into this concept. Their lack of an oxygen function at C-6 perfectly corresponds to a joint biogenesis of both molecular halves of 29 from the same, less oxygenated diketone 32—a remarkably economical, converging biosynthesis which, despite the structural diversity of the two molecular moieties 34 and 35, manages with only the one monocyclic precursor 32. 

Following the postulated biogenetic pathway (see Scheme 3), a chemical in vitro imitation, aiming at a biomimetic first synthesis of naphthyl isoquinoline alkaloids, had to consist of essentially four crucial steps (1) synthesis of suitable P-polycarbonyl precursors, (2) their primary cyclization to monocyclic diketones like 31 or 32, (3) the further differentiation to naphthalenes and isoquinolines, and (4) their mixed coupling to the complete natural alkaloids. 

Nonetheless, this strategy was taken up again (54,56). After an improved synthesis of the dihydroindane 56, cleavage to 57 was carried out using 02-free (59) ozone (Scheme 10). Ring closure could now be brought about very smoothly with various nonnucleophilic bases, more simply, but silica gel-catalyzed by a short column filtration, and indeed gave the desired monocyclic diketone 58. 

For future labeling syntheses of potential biosynthetic precursors, as well as for preparation of monocyclic diketones 70, on a 100- to 1000-g scale, additional, nonbiomimetic syntheses to these important intermediates were elaborated (63) (see Scheme 14). The key step of the first synthesis was oxidative cleavage of suitably substituted dimethyl indenes 68, either directly with permanganate-periodate or via remarkably stable ozonides 69. The required indenes 68 could be prepared from esters 67, and thus from very cheap educts like methacrylic acid and... 

Figure 27 Reduction of monocyclic p-diketones with yeasts.

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