Ketones precursors

Some advantages of this reaction are high yield if the tosylate is in a sterically accessible position excellent isotopic purity of the product (usually higher than-95%) and perhaps most important, access to stereospecifically labeled methylene derivatives. For example, deuteride displacement of 3j -tosylates (183) yields the corresponding Sa-d derivative (185) in 96-98% isotopic purity. Application of this method to the labeled sulfonate (184), obtained. by lithium aluminum deuteride reduction of a 3-ketone precursor (see section HI-A) followed by tosylation, provides an excellent synthesis of 3,3-d2 labeled steroids (186) without isotopic scrambling at the adjacent positions. The only other method which provides products of comparable isotopic purity at this position is the reduction of the tosyl-hydrazone derivative of 3-keto steroids (section IV-B). 

Methyl vinyl ketone 2 tends to polymerize, especially in the presence of a strong base the yield of annulation product is therefore often low. A methyl vinyl ketone precursor, e.g. 6, is often employed, from which the Michael acceptor 2 is generated in situ, upon treatment with a base. The quaternary ammonium salt 6 can be obtained by reaction of the tertiary amine 5, which in turn is prepared from acetone, formaldehyde and diethylamine in a Mannich reaction. 

Problem 23.5 Which of the following compounds are aldol condensation products What is the aldehyde or ketone precursor of each ... 

Synthetic applications of other decarbonylation reactions are found in the conversion of cyclooctatetraene to barrelene 250), with the photodecarbonyla-tion of a Diels-Alder adduct as key step (2.31) and the preparation of tetrathioesters from 1,3-dithioles (2.32) 251). The most remarcable application of such a reaction up to date is the synthesis of tetra t.butyltetrahedrane from a tricyclic ketone precursor (2.33) 252). 

Although harmine 52 is frequently obtained by isolation (or purchase order), a synthesis of this compound as well as a number of analogs has recently appeared [47,48]. The key step to this synthesis was the thermal electrocyclization of oxime intermediate 55, which was prepared by acylation of vinylindole derivative 54 followed by treatment with hydroxylamine hydrochloride. Neither oxime 55 nor its ketone precursor were isolated— instead, the crude reaction mixture was heated at reflux in o-dichlorobenzene to ultimately yield harmine in 56% yield overall starting from 54 (Fig. 18). 

With a-A3-iodanyl ketone precursors. Exposure of (2-acetoxyvinyl)phenyl-A3-iodanes 369 to 2-imidazolidinethione and triethylamine in methanol produced the bridgehead heterocycle 370 of type 5,6-dihydro-imidazo[2,l-3]thiazoles (Equation 166) <2003JOC7887>. 

Dialkylquinazolines 825 are available by microwave-assisted amination and ring closure of 2-acylamino phenyl-ketones 824 with ammonium formate <20070L69>. The 2-aminophenyl ketone precursors of the amides 824 are available by a photochemically induced Fries rearrangement of anilides 823, which enables a variety of different alkyl substituents to be incorporated at the 4-position of the quinazoline <20070L69>. 

The development of chiral ketone precursors for asymmetric induction in dioxirane-promoted epoxidations has been the subject of intense and fruitful study in recent years, and Denmark and Wu have recently published a very useful review on the topic <99SL847>. One such chiral ketone... 

The key step in their-approach was asymmetric photoisomerization of the a, 3-unsaturated (Z)-ketone precursor 103b in diethyl ( + )-Lg-tartrate. The bromide 103a obtained by N-bromo-succinimide bromination of the (Z)[8.8] precursor 64b, was converted into the a,P-unsaturated (Z)-ketone 103b by the routine synthetic procedures. Irradiation in a hexane solution with a medium pressure Hg lamp effected the photoisomerization of the (Z)-precursor 103b to afford a 1 5.5 mixture of (Z)-( )[8.8] ketones. After these preliminary experiments, a neat solution of 103 b in diethyl ( + )-Lg-tartrate was irradiated for 3 h. Preparative GLC of the resulting 1 7 mixture of (Z) and ( )[8.8] ketones produced a 38 % yield of ( )[8.8] ketone 104 enriched in the (—)-enantiomer, [a]n4 —13° (hexane). 

Much of the value of this route lies in the ready availability of the ketone precursors and in the variety of conditions which may be used to effect cyclization. 

The oxidation of alcohols to carbonyl compounds is one of the most relevant transformations in organic synthesis, due to the large diversity of products that can be obtained from aldehyde and ketone precursors. 

An interesting paper reports the combined synthesis of 3-vinylindoles from ketones with the vinylindole synthesis of tetrahydrocarbazoles in one flask by using indole (1 equivalent) and excess ketone precursor as the solvent, usually at reflux with maleic acid (1 equivalent), both as the catalyst for 3-vinylindole formation and as the dienophile for the Diels-Alder reaction. These reactions constitute an in situ vinylindole synthesis of tetrahydrocarbazoles (79JOC4402). 

In each part of this problem in which there is a change in the carbon skeleton, disconnect the phenyl group of the product to reveal the aldehyde or ketone precursor that reacts with the Grignard reagent derived from bromobenzene. Recall that reaction of a Grignard reagent with formaldehyde (H2C=0) yields a primary alcohol, reaction with an aldehyde (other than formaldehyde) yields a secondary alcohol, and reaction with a ketone yields a tertiary alcohol. 

In recent work (2008) ultrafast photolysis of a potential diazo ketone precursor of p-biphenylmethyloxirene failed to detect the oxirene, the UV absorption of which could, however, have been hidden by another band [8], and in a combined experimental/computational (ab initio and molecular dynamics with DFT) study, flash thermolysis of a formal Diels-Alder adduct was interpreted as affording acetylmethyloxirene and benzene [9]. 

As shown in Scheme 8, a common ketone precursor led to the pyrazolo[4,3- ]- and thiazolo[5,4- ]-fused 1,4-benzoxazines (96) and (97) <87JMC580>. For the synthesis of compound (96) the ketone was condensed with HC02Et and subsequently cyclized with hydrazine. For the synthesis of the thiazole (97) a-bromination of the ketone was followed by condensation with thiourea. The linear tricyclic structures (96) and (97) were supported by H and 13C NMR spectroscopic analyses. 

A catalytic tandem conjugate addition-aldol cyclization950 allowed the formation of five- and six-membered ring products from aromatic and aliphatic ketone precursors (Equation (218)).974... 

Isomerization of the ketone precursor is brought about by a reversible reaction with the basic Wittig reagent, which yields an equilibrium mixture of two diastereomeric ketones. One of the ketone isomers then reacts preferentially with the Wittig reagent to give only the observed product. 

Look at the target molecule to find the groups bonded to nitrogen. One group comes from the aldehyde/ketone precursor, and the other group comes from the amine precursor. In most cases, two combinations of amine and aldehyde/ketone are possible. 

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