McCormack reaction

The 2- and 3-phospholenes are prepared by the McCormack reaction and are good candidates as starting materials for the preparation of five-and six-membered phosphorus heterocycles [25-27]. From l-methoxy-3-methyl-2-phospholene 64 or l-methoxy-2,3-diacetoxy-3-methylphospholane 67, l-aryoxy-3-methyl-2-phospholenes 66a-c (Scheme 19), or l-aryoxy-2,3-diacetoxy-3-methylphospholane 69 (Scheme 20) with a substituted phenyl group at phosphorus, or l-aryl-3-methyl-2-phospholenes 71a-g (Scheme 21) are prepared by a substitution reaction and/or a Grignard coupling reaction [28,29]. 

Tetramethyl-l,l -diheteroferrocenes 21 have been prepared by a modification of the McCormack reaction, based on the fact that the starting diiodide 66 could be stereospecifically desilylated with BU4NF/H2O to afford 67 in 86% yield. Lithiation of diiodide 67 with butyllithium followed by reaction with dichlorophenylarsine or dichlorophenylstibine, respectively, yields the target compounds 68 (X = As, Sb). Unfortunately, the reaction failed for the bismole derivative preparation (Scheme 12) <1995AGE295>. 

The isolation and characterization of chloroaluminate complexes of the type [CgHigP ClR] [AICI4"], by other workers from reactions which involved phosphonous dihalides, RPCI2, seemed to confirm suggestions as to the reaction mechanism, and which are summarized in Scheme 6. As originally envisioned, the mechanism required the initial complexation of PCI3 and AICI3, a point in doubt, but it may be noted that the proposed intermediate 122 possesses a chlorophosphonium structure similar to that encountered in the McCormack reaction. 

Quin s group have reported the synthesis of a number of tricyclic phospholene oxides, e.g., (9), by the McCormack reaction. The isomeric bicyclic phosphine... 

Dihydro derivatives of phospholes, commonly referred to as phospholenes, are easily prepared and known in great number. The oxides are especially well studied, the result of a highly versatile and simple synthetic procedure (the McCormack reaction) being available. 

The phospholene oxides resulting from the McCormack reaction also serve as highly useful starting materials for the synthesis of phospholane oxides by simple hydrogenation techniques (Equation (47)). 

No other synthetic method for phospholene oxides approaches the McCormack reaction in simplicity and versatility. Some specialized methods do exist, however. One is shown here that allows 2,2-disubstitution in the phospholene ring, which cannot be obtained with the McCormack method (Scheme 55). 

Phospholene oxides from the McCormack reaction also stand as useful precursors of phos-pholanes as noted, the double bond can be easily hydrogenated, and then the oxygen removed from phosphorus with silanes, etc. (Schemes 56 and 57 Equations (51) to (53)). Phospholanes can be prepared by other cyclization methods, however, some of which are outlined below. 

It is also possible to place a variety of alkyl substituents on phosphorus of the phospholene system by preparing the P-halo derivative and reacting it with organometallic derivatives. Several phospholes have been prepared by this approach (Scheme 72) <73JOCl858>. An obvious advantage is that the need for the alkylphosphonous dichloride required in a McCormack reaction is eliminated. The dichlorides are difficult to prepare and handle. 

The P-phenyl group of a phosphole can be directly displaced by reaction with alkyl lithium reagents in TMEDA. Both t-butyl <72T47i> and -butyl <720MR(4)171> have been placed on P by this method. With 3,4-dimethyl-1-phenylphosphole, the former reaction occurred in 70% yield, the latter in 31.5% (with some oxide) (Scheme 79). This method is of considerable value for the introduction of the t-butyl group on phosphorus, as this group cannot be used as the P-substituent in a phosphonous dihalide in the McCormack reaction because of steric restrictions. 

Unfortunately, arsenic, antimony, or bismuth chemistry has no reaction analogous to the McCormack reaction for the synthesis of phospholenes and phospholes (see Section 2.15.10.3). 

Synthesis of phospholes via the McCormack reaction. Phos-phole derivatives are recognized as valuable precursors for the preparation of a variety of optoelectronic devices, which explains the upsurge of interest in the synthesis of these species in the recent literature. 

In the recent past, Keglevich and coworkers demonstrated the synthesis of several phosphole derivatives (74) based on the McCormack reaction,followed by microwave-assisted esterification of the phosphinic acid using different alcohols in yields up to 94% (Scheme 34). ... 

The phospholium salts (1) are available from the McCormack cycloaddition of butadiene derivatives with phosphonous dihalogenides (Route A/Scheme 2) [26-28], from quatemization of chlorophospholenes (3) with alkylhalogenides (Route B/Scheme 2) [29] or from the reaction of alkylphospholenes (4) with bromine or chlorine (Route C/Scheme 2) [29], In the latter case, the halogen reacts selectively with the phosphorus atom. 

Reactions. - The reactions of diorganoiodophosphines with varying quantities of iodine have been studied by NMR techniques, which indicate the formation of a dialkyldi-iodophosphonium iodide as the initial product, followed by polyhalide anion formation in the presence of excess iodine. A modified McCormack synthesis of 3-silylated phosphol-3-enes (168) from phenyl-dichlorophosphine and 2-silylated 1,3-butadienes has been described. The reaction is carried out in the presence of a small amount of copper stearate in acetic anhydride at 50 °C, these conditions preventing the complete desilylation observed under standard conditions. The consecutive reaction of lithium phenylacetylide with triphenylborane and diphenylchlorophosphine results in the formation of the intramolecularly coordinated phosphino-borane (169). Treatment of the alkoxyvinyldichlorophosphines (170) with Grignard reagents... 

It was McCormack who, in 1953, in the patent literature, first reported the cycloaddition of phosphorus(III) halides to l,3-dienes . As then represented, the sequence took the form depicted in reaction 13 (X = Cl or Br). The careful addition of water to the crystalline 1 1 adduct, formulated as a halogenophosphonium salt (92), gave the unsaturated phosphinic chloride (93, R = Br or Cl) or acid (93, R = OH). Since the original publication of the procedure, the application of modern spectroscopic techniques has demonstrated that the final products in such reactions are mixtures of the 3-phospholene (93) and 2-phospholene (94) isomers, conveniently represented, when admixed and in unknown proportions, as 95. It has since become apparent that the relative proportions of the isomeric forms 93 and 94 of any derivative depend on the nature of the halogen X and on the manner of work-up thus, in an acidic work-up medium, the products tend to have the structure 94, but neutralization during the hydrolysis step leads to derivatives of the isomeric 93. The reaction consists simply in mixing the reactants at room temperature and... 

With an acid whose anionic part has some nucleophilic character, such as HCl, a secondary reaction occurs. The P-protonation in CD2CI2 at —90°C can be detected by P NMR but on warming to — 70 °C the P—H form disappears and a signal for the l-chloro-2,5-dihydrophospholium ion (68) appears. This substance is the same as formed in the McCormack cycloaddition of dienes and RPCI2 (see Section 2.15.8.2) and is easily recognized (Scheme 6). 

Phospholenes generally have an envelope-shaped conformation (6.884). The most versatile method for the synthesis of phospholenes is the McCormack cycloaddition reaction using a diene and a phosphonous dihalide or a phosphorus trihalide [63,64]. 

Somers MF, McCormack DA, Kroes GJ, Olsen RA, Baerends EJ, Mowrey RC (2002) Signatures of site-specific reaction of H2 on Cu(lOO). J Chem Phys 117 6673... 

A soln. of phenyldichlorophosphine and commercial isoprene containing lonol (2,6-di-fert-butyl-p-cresol) as antioxidant allowed to stand 5-7 days at room temp, in a stoppered flask, the resulting 1,1-dichloro-1-phenyl-3-methyl-1-phospha-3-cyclopentene stirred into ice-water, and stirring continued until essentially all of it is dissolved 3-methyl-l-phenyl-l-phospha-3-cyclopentone 1-oxide. Y 57-63%.—This is a general reaction, and there can be a wide variety of alkyl, aryl, and halogeno substituents on the diene and phosphorus. W. B. McCormack, Org. Synth. 43, 73 (1963). 

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