Regioselectivity preparation

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

Perhydropyrido[l,2-A][l,2]oxazines are applied as key intermediates in a stereospecific total syntheses of (-)-pumiliotoxin C and 5-e/ /-pumiliotoxin C(96JCS(P1)1113), and the marine alkaloid)—)-lepadins A, B, C (OOOL2955). (2-Pyridyl)propionic acids 13 can be regioselectively prepared via 2,3,4, 4fl,7,8-hexahydropyrido[l,2-A][l,2]oxazin-2-ones 12 (00OL4007). 

The alkenyl triflates can be prepared from ketones,200 and methods are available for regioselective preparation of alkenyl triflates from unsymmetrical ketones.201... 

C02Me)CH2-C02Me was regioselectively prepared in >82% enantiomeric excess by homogeneous catalytic hydroformylation. For other vinylidene esters, the asymmetric induction was lower.318... 

The regioselective preparation of 2-substltuted naphthalenediol derivatives having the diols differentially protected in a predictable and straightforward manner, previously not directly attainable, is readily accomplished using chromium carbene complexes. First prepared by E. O. Fischer, chromium carbene complexes react readily with alkynes (extensively investigated by K. H. D6tz, and others).3 Steric effects dictate the substitution pattern observed2-4 and the reaction mechanism has been widely studied.2... 

The electrochemical oxidation of l-MeO-7-alkyl-CHT in MeOH yields 2-alkyltropones, while the thermal rearrangement of 3-MeO-7-alkyl-CHT to l-MeO-4-alkyl-CHT followed by its anodic oxidation in MeOH affords 4-alkyltropones (equation 21). l-MeO-7-alkyl-CHT is prepared by the regioselective alkylation of 7,7-diMeO-CHT with a Grignard reagent and Cul, while 3-MeO-7-alkyl-CHT is also regioselectively prepared by alkylation of 7,7-diMeO-CHT with an alkyl lithium. 

Iron-Catalyzed Reactions of Grignard Reagents TABLE 1. Regioselective preparation of trimethylsilyl enol ether... 

Using similar techniques, Suda et al. have fluorinated a series of 4-trimethyl-silylazetidin-2-ones in an efficient and regioselective preparation of 4-fluoro-azetidin-2-ones [45]. 

Vicinal fluoro methoxy compounds, e.g. 32 and 33, are regioselectively prepared in high yield from vicinal methoxy chloromercurio derivatives by reaction with acetyl hypofluorite.29... 

Details of the regioselective preparation of a variety of new 2,4-disubstituted oxazoles, using both iodide- and acid-promoted rearrangements of TV-acylaziridines, have been presented.584 It has been shown585 that two plausible mechanisms (S i and/or two 5n2 reactions) can account for the acid-catalysed transformation of 1-acylaziridines (447) to oxazolines (448), while the regioselective rearrangement of... 

Alkenyliodonium salts can be used as highly reactive substrates for Heck-type olefination and similar palladium-catalyzed cross-coupling reactions [63 -65]. In a recent example, a series of dienes 80 were stereo- and regioselectively prepared by a palladium-catalyzed Heck-type reaction of alkenyliodonium salts 79 with a,/3-unsaturated carbonyl compounds (Scheme 37) [64]. 

The same technique can be applied to regioselectively prepare 4-alkoxy substituted azetidinones. Non-silylated azetidinones have oxidation potentials, which are too high for this process. Introduction of a silyl group lowers these potentials, rendering the reaction easier and more regiospecific. Note that in the case of /V-benzyl azetidinones, the methoxylation reaction occurs also at the benzylic position.12213 355... 

Fig. 13.14. Regiosetective generation of ketone enolates III the effects of conjugated versus nonconjugated substituents (for the regioselective preparation of enotate B, see Figure 13.21).

Fig. 10.10. Regioselective generation of ketone enolates II the effects of different substituents in the ft and [V positions. (For the regioselective preparation of enolates C and F, see Figures 10.16 and 10.17, respectively.)...

The next four procedures describe the regioselective preparation of bicyclic ring systems, specifically, condensed five-membered carbocyclic derivatives. A large... 

A number of additional cyclizations involving alkynes have been reported. For instance, it has been shown that indoles may also be accessed from 2-bromo- or 2-chloroanilines, as illustrated by the regioselective preparation of the carbinol 373 in the presence of the ferrocene 374 (Equation 104) <20040L4129>, whereas a one-pot sequence featuring titanium catalyzed hydroamination of 2-chloroanilines with acetylenes, followed by intramolecular Heck cyclization in the presence of an imidazol-2-ylidene palladium complex, has also been reported <2004CC2824>. A set of aryl-2-indolyl carbinols have been prepared in high enantiomeric purity by palladium-catalyzed annulation of... 

Two types of 3-benzoylbenzo[7]furans were regioselectively prepared from their corresponding starting materials 2-methylbenzo[ ]furan and 2-benzylbenzo[7]furan through a Friedel-Crafts reaction pathway, as shown in Scheme 47 <2002JME623>. 

Scheme 10.2 Regioselective preparation of carbamate derivatives of 2 -deoxynucleosides.

LDA prepared in this way is recommended for regioselective preparation of the less thermodynamically stable enol ether and for generation of dianions of carboxylic acids. The reaction of dianions prepared with this base with aldehydes provides a stereoselective route to y,8-unsaturated p-hydroxy carboxylic acids (equation II). 

Primary amines have been transformed into imines which when metallated react with carbonyl compounds. Treatment with butyllithium, alkylation with allyl bromide and hydrolysis gives highly substituted aldehydes (Scheme 6). Thus, in this example, the carbon adjacent to the original amino nitrogen atom becomes the carbonyl carbon. The technique has been used several times in the course of total synthesis, as with a recent approach to crinine and as the key step in a recent highly regioselective preparation of a,3 unsaturated aldehydes (equation 33). ... 

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