General Route

Alkyl sulphuric acids are known to be as acidic as sulphuric acid itself and to form inorganic salts readily [13]. In the general procedure [11], the sulphur trioxide/pyridine complex, in excess, and the respective carotenol are mixed at -10°C and the reaction, monitored by TLC, is allowed to proceed at room temperature. The reaction is quenched either by the addition of 10% aqueous NaOH to ca. pH 9, or by the addition of an aqueous NaCl solution. The carotenoids are extracted with ethyl acetate (or for disulphates with chloroform-methanol) from the aqueous hypophase and separated by TLC. 

The pigment recovery is generally around 75%, and unreacted carotenol comprises around 20% of the recovered carotenoids [11]. 

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A more general route to three-membered rings is based on a new type of disconnection the removal of an atom... 

Intramolecular reactions between donor and acceptor centres in fused ring systems provide a general route to bridged polycyclic systems. The cts-decalone mesylate given below contains two d -centres adjacent to the carbonyl function and one a -centre. Treatment of this compound with base leads to reversible enolate formation, and the C-3 carbanion substitutes the mesylate on C-7 (J. Gauthier, 1967 A. Belanger, 1968). 

Unsyimnetiical rhodainines can be piepaied by the condensations of one mole of a yW-aminophenol with phthahc anhydride to give an o-benzoyl benzoic acid (27) which is then further condensed with a different yW-aminophenol to give the requited product, Rhodamine 3GO (28) (2). A general route to asymmetrical acid xanthenes has been patented (39). 

Although details vary for particular cases, a common synthetic route to diol epoxides such as (30) frequently begins with the ketone (33) (78MI50700). The final epoxidation is often highly stereoselective. A general route to non-K-region arene oxides has been described (75JA3185). 

Several ring contraction routes to /3-lactams have been developed. One of the most important is the photochemical Wolff rearrangement of 3-diazopyrrolidine-2,4-diones (178), which provides a general route to 3-carboxyazetidin-2-ones (179). Lack of stereoselectivity is a problem, but facile epimerization is possible because of the electron withdrawing 3-substituent (78T1731). 

It is often necessary to prepare /3-lactams with particular substituents at N-1, C-3 and C-4, e.g. in the preparation of fused /3-lactams from monocyclic precursors. For reasons of space it is not possible to give an exhaustive list of the variously substituted /3-lactams available however, Table 4 summarizes the most general routes to /3-lactams bearing particular substituents at C-3 and C-4. -Substitution of azetidin-2-ones has already been dealt with cf. Section 5.09.3.2.3). N-Unsubstituted /3-lactams and protected 3-amino-/3-lactams are particularly important synthetic intermediates and methods of preparing these are discussed below. 

This procedure illustrates a general method for the preparation of 2-hydroxybicyclo[3.2.0]heptanes by copper(I)-catalyzed photobicyclization of 3-hydroxy-1,6-heptadienes, and a general route to the requisite dienes from allyl alcohols by conversion to 4-pentenals and treatment of the latter with vinyl Grignard reagents. 

There are three general routes for producing intermediates from petroleum ... 

Action of anhydrous neutral alumina on gem-difluorocycloalkanes (see section VI) is a convenient general route to cyclic vinyl fluorides. ... 

Iodine cleavage of 2,2-difluoroalkenylboranes provides a general route to l-difluoro-2-iodoalkenes [49] (equation 32)... 

Many reactions of fluorinated organics with metal halides result in the replacement of fluorine with halogen A general route to 1,1,1-trichloro- or tribromo-fluoroalkanes involves treating primary fluoroalkyl iodides with aluminum trichloride or aluminum tribromide [74], Benzylic [75, 76] or vinylic [72] fluorine can be exchanged for chlorine when treated with aluminum trichloride... 

A general route to benzo-2,l,3-selenadiazoles involves the condensation reaction between 1,2-diaminobenzene and selenium tetrachloride. This method has also been used recently for the synthesis of 4,5,6,7-tetrafluoro-2,l,3-benzotelluradiazole (Eq. 2.9) ... 

There are two general routes to complexes. The first involves direct addition of molecular Ht either to an unoccupied coordination site in a 16-electron complex (as above) or by displacement of a ligand such as CO, Cl, H2O in the coordination sphere of an 18-electron complex in this latter case ultraviolet irradiation may be required to assist in the... 

Variation in eurrent, voltage and eleetrolyte eomposition frequently results in the formation of phosphides of different stoiehiometries. Less-general routes (whieh are nevertheless extremely valuable in speeifie instanees) inelude ... 

The first such compound to be prepared was the deep-yellow unstable compound 9-arsa-anthracene but the thermally stable colourless arsabenzene (arsenin) can now conveniently be made by a general route from l,4-pentadiyne ... 

Anhydrous polythionic acids can be made in ether solution by three general routes ... 

The most general route to 1,2,3,4-thiatriazoles involves treatment of a thiohydrazide with nitrous acid [Eq. (1)]. Thus, 5-amino-... 

The A-phthalimidomalonic ester 8 can be further alkylated at the malonic carbon center with most alkyl halides, or with an o ,/3-unsaturated carbonyl compound thus offering a general route to a-amino acids 9. 

More useful for synthetic purposes, however, is the combination of the zinc-copper couple with methylene iodide to generate carbene-zinc iodide complex, which undergoes addition to double bonds exclusively to form cyclopropanes (7). The base-catalyzed generation of halocarbenes from haloforms (2) also provides a general route to 1,1-dihalocyclopropanes via carbene addition, as does the nonbasic generation of dihalocarbenes from phenyl(trihalomethyl)mercury compounds. Details of these reactions are given below. 

The treatment of 1,1-dihalocyclopropanes by methyllithium appears to be a general route to allenes, providing the product is not highly strained. An example is shown in the reaction (13). The procedure given below employs the reaction for the preparation... 

Kaeriyama and Shimura [34] have reported the photoinitiation of polymerization of MMA and styrene by 12 metal acetylacetonate complex. These are Mn(acac)3, Mo02(acac)2, Al(acac)3, Cu(bzac)2, Mg(acac)2, Co(a-cac)2, Co(acac)3, Cr(acac)3, Zn(acac)2, Fe(acac)3, Ni(a-cac)2, and (Ti(acac)2) - TiCU. It was found that Mn(a-cac)3 and Co(acac)3 are the most efficient initiators. The intraredox reaction with production of acac radicals is proposed as a general route for the photodecomposition of these chelates. 

Electrochemical fluorination of cyclic 2-(dialkylamino)-propionic acids provides a general route to optically active perfluoro-(2-cycIic(dialkyl-amino)-propionic acids [91 JFC(52) 133], which are a source of perfluorinated vinylamines (88CL1887). 

Reaction of ethyl (V-(cyanoacetyl)urethane with trifluoroacetonitrile gave 5-cyano-6-trifluoromethyluracil (85JOC4642). Trifluoroacetonitrile reacted with benzyl cyanide (86JOU1408) and diethyl malonate (89JHC7) to yield 2,6-bis(trifluoromethyl)pyrimidines. Cycloaddition of trifluoroacetonitrile with enamines having a /3-H offered a general route to 2,4-bis(trifluoromethyl)pyrimidines (84LA991). 

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

Among the a-hetero-substituted chiral organometallic reagents, a-lithio ethers 2 are an important class of compounds. A general route to these compounds is the reductive lithiation of a-(phcnylthio) ethers 1 with lithium (dimethylamino)naphthalenide (I.DMAN)4,5. The generality of this method lies in the ready availability of various types of a-(phenylthio) ethers. 

Other RhCl(CO)(PR3)2 compounds (PR3 = PEt3, PBu3, Palkyl2Ph, PalkylPh2, P(OR)3, PBu2 alkyl) have been synthesized by the general route... 

Complexes with other phosphines can be prepared by the general route of refluxing IrCl3 or IrClg- in an alcohol that acts as the source of CO, then adding the phosphine. In certain cases, a displacement reaction can be used... 

Other less general routes to the medium-size ring sulfoxide and sulfone systems do exist, but each one is specific to a particular ring size and to the specifically desired structural features of the target molecule. Equations 131 and 132 are two examples353,354 of such syntheses. 

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