Phosphorinanes

Phosphorinanes (phosphinanes) always exist in the chair form, which means that axial or equatorial isomers can be present. Crystal structure studies of numerous derivatives have confirmed the rings are chair-shaped with the exocyclic group attached to phosphorus in the axial position. From NMR studies it appears that mainly the axial form is present in parent phosphorinane, and in methylphosphorinane, at ordinary temperatures, as is the case with piperidine (6.807). At low temperatures the proportion of the equatorial form increases. 

Phosphorinanes were first obtained in 1915 using reaction [23] 

Phosphorinane (phosphinane), (CH2)5PH, mp = 19°C, bp = 118-121°C, can be made by the route indicated in scheme (6.809) starting with 1 5 dibromopentane and tributyl phosphite. This leads first, via an Arbusov-type reaction, to the butyl ester of 5-bromopentyl phosphonic acid, which, when treated with magnesium bromide, yields the cyclic ester, which in turn is hydrolysed by boiling acid to give 1-hydroxyphosphorinane 1-oxide. This latter compound can then be reduced with diphenylsilane. 

Phosphorinane is a colourless, malodorous toxic liquid which readily inflames in air. It is configurationally more stable than piperidine, in which the two isomers can be interconverted by inversion at the N atom, at a temperature as low as -fiO C. At -SO C, when pyramidal inversions are slowed down, the methyl groups lie largely in the equatorial positions in methyl piperidine (95%) methylcyclohexane (99%) and methylphosphorinane (66%). 

Careful oxidation of phosphorinane in dilute petroleum solution gives 1,T diphosphorinane 1,T dioxide, while oxygen under aqueous conditions gives phosphorinane 1 oxide. The latter compound may also be obtained from the phosphinic acid as indicated in (6.809). Treatment of phosphorinane with sulphur in boiling benzene leads to 1 mercapto phosphorinane 1 sulphide which in turn readily converts into the disulphide. 

The H-nmr spectrum of phosphorinane (1) indicates that the proton on phosphorus is axial and gives no evidence of the presence of an equatorial isomer. Similar conclusions are drawn from the spectrum of phosphorinane 1-sulphide (2), but no conclusions can be reached concerning the proton on the phosphorus of phosphorinane methiodide (3) because of second--order spectral complications (J.B. Lambert and W.L. Oliver, Tetrahedron, 1971, 27, 4245). 

Investigation of the conformational equilibrium of 1-methyl-phosphorinane (4) by low temperature and P-nmr shows a temperature dependence, favouring the equatorial methyl conformer at low temperature and the axial methyl one at room temperature (S.I. Featherman and L.D. Quin, J. Amer. chem. Soc., 1973, 95, 1699). 

A mixture of ais- (5) and tvans- (6) 1-phenyl-4-tert--butylphosphorinane 1-oxide, m.p. 160-161° and 88.5-95°, respectively, is obtained on boiling 1,1-diphenyl-4-tert--butylphosphorinanium bromide with M sodium hydroxide for a long time. The isomers have been separated and converted by phenylsilane reduction into cis- and trans-l-phenyl-4-tei f--butylphosphorirane, each with a b.p. 110-120 /0.1 mm. 1,1--Diphenyl-4-tf ans-butylphosphorinanium bromide on treatment with aqueous sodium hydroxide yields a mixture of (5 60%) and (6 40%) (K.L. Maris et at, J. org. Chem., 1977, 42, 1306). Studies of phosphorus inversion in and conformational analysis of ais- and l-phenyl-4-tef t-butylphosphorinane have been 

Radical addition of trimethylsilylphosphine to 1,4--pentadiene affords the synthon 1-trimethylsilylphosphorinane, hydrolysis of which gives phosphorinane in quantitative yield (D.M. Schubert and A.D. Norman, Inorg. Chem., 1984, 4130). 

1-Methylphosphorinane forms a 1 1 and a 1 2 adduct with bromine and with iodine, but only a 1 1 adduct with chlorine (Lambert and H.-n. Sun, J. org. Chem., 1977, 42,1315). 

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When immediately followed by -in or -ine, phospha- should be replaced by phosphor-, arsa- by arsen-, and stiba-by antimon-. The saturated six-membered rings corresponding to phosphorin and arsenin are named phosphorinane and arsenane. A further exception is the replacement of borin by borinane. 

Phosphorinane, 4-t-butyl-1 -phenyl-synthesis, 1, 500 Phosphorinane, I-chloro-synthesis, 1, 500 Phosphorinane, 1-hydrocarbyl-I-sulfide synthesis, 1, 500 Phosphorinane, 1-phenyl-synthesis, 1, 499 Phosphorinanes, 1, 497-506 bicyclic bridged derivatives synthesis, 1, 501 conformation, 1, 503-504 NMR, 1, 497 oxidation, 1, 498 reactions, 1, 497 structure, 1, 497, 503-504 sulfuration, 1, 499 synthesis, 1, 499... 

C. By Reduction.—The cyclic secondary phosphines phospholan and phosphorinan have been prepared by reduction of the corresponding chlorophosphines with lithium aluminium hydride. ... 

N.m.r. spectroscopy has played an important part in determining the stereochemistry of the 1,3-dioxaphosphorinanes (52). The presence of the saturated six-membered ring means that there are usually conformational effects to be unravelled before configurational assignments can be made. The chair conformation is generally dominant. Phosphorus substituents which exhibit shielding effects show that in many P " phosphorinanes this substituent occupies an axial position and Sis( has been used to establish the equatorial conformation of a t-butyl substituent at C(5). Even in P" derivatives the isomer possessing the bulkiest P-substituent in an axial... 

Unlike the late metal chemistry reviewed above, these reactions did not require Michael acceptor substrates, but the reactions were rather slow (turnover frequencies range from 2 to 13 h at 22°C). For phosphino-alkenes (Scheme 5-15, Eqs. 1-3), a competing uncatalyzed reaction gave six-membered phosphorinane rings (Scheme 5-15, Eq. 6) this could be minimized by avoiding light and increased temperature. For phosphino-alkynes (Scheme 5-15, Eqs. 4 and 5), the products were unstable and could not be isolated [14]. 

Scheme 5-15 Examples of organolanthanide-cat-alyzed hydrophosphina-tion/q clization. Eq. (6) Phosphinoalkenes can undergo organolanthanide-catalyzed hydrophosphi-nation/cyclization to give phospholanes or an uncatalyzed reaction to give phosphorinanes...

The geminal coupling of some azo1ooxaphospho1enes is reported to correlate with A.. 9 1 Vicinal couplings have been used in the conformational analysis of a variety of compounds such as dioxaphosphorinanes,92 phosphorinanes (in combination uith CNDO/2 calculations),93 and bromophosphorinanes (in combination uith dipole moment measurements).99 The various couplings for 1,1-viny1idene-diphosphonic acid and its salts have also been measured.95... 

Two heterocyclic systems have been investigated - the 1,3,2-dioxaphosphepene (45) and its oxide,13 1,3,2-dioxa-phosphorinanes and their oxides, sulphides and selenides (46).136,137 Three ring vibrations were involved in the conformational study of the amides (46, Y = NR2).137... 

In the hydrolysis of neutral tricyclic hexacoordinate spirophosphorane 143 with internal N—>P dative bonds, the six-membered phosphorinane ring is retained during the first stage of hydrolysis. Five-, seven-, and eight-membered rings were preferentially hydrolysed (Equation 4) <1998POL3643>. 

The interaction of cyclic aminomethylphosphines may proceed either with opening of the ring or with its preservation (89IZV1375). 1,3,5-Diaza-phosphorinane (43) with R = C6H4Me-p at the nitrogen atoms, when treated by diborane, opens its ring with rupture of the C—N bond in the N—C—N fragment and coordination of the borane molecule at the phosphorus atom [Eq. (47)]. 

Unlike 1,3,5-dioxaphosphorinanes the relative population of the con-former with the axial phenyl group at phosphorus decreases in 1,3,5-diazaphosphorinanes both for P(III) and for P(IV) compounds. Conformational analysis of 5-phenyl-1,3,5-diazaphosphorinanes and their oxides, sulfides, and selenides showed that the conformational equilibrium shifted toward the conformer with the axial phenyl group on changing from P(III) to P(1V) derivatives. The same conclusion made for 5-phenyl-l, 3,5-dioxaphosphorinanes, but it is contrary to that made for 1-phenyl-phosphorinane-4-ones and their derivatives (83MI1). 

In the case of boric acid, the products with two 1,3,2,5-dioxabora-phosphorinane rings (97), (98) are obtained as water was removed azeo-tropically [Eq. (57)] (85IZV1102). 

Tertiary amines or pyridine reacts with diphenylboryloxyalkyl(a-oxyal-kyl)phenylphosphine sulfide to give the corresponding ammonium dioxa-borataphosphorinanes [Eq. (114)] (83IZV2545). Ammonium dioxaborata-phosphorinane was obtained by refluxing betaine 104 in triethylamine [Eq. (115)] (92IZV1398). 

Gusarova, N.K., Shaikhudinova, S.I., Dmitriev, V.I., Malysheva, S.F., Arbuzova, S.N., and Trofimov, B.A., Reaction of red phosphorus with electrophiles in superbasic systems. VII. Phospholanes and phosphorinanes from red phosphorus and a,co-dihaloalkanes in a single preparative step, Zhur. Obshch. Khim., 65, 1096, 1995. 

Gallagher has reported a convenient synthesis of functionalized phosphorinans (102) by Michael addition of methyl hypophosphite to methyl acrylate, followed by base-induced cyclization.78... 

The addition of oxygen, sulphur, or selenium to 2-hydro-4-methyl-l,3,2-dioxa-phosphorinan proceeds stereospecifically.143... 

In relation to the consideration of the stereospecificity of coupling in Pm compounds, an observation of Kainosho<1969,95) seems especially important. Complexing the phosphorus atom by addition of a paramagnetic ion removes any stereospecific phosphorus couplings. In the phosphorinane 55a, 3J(POCHA) = 2-2 and aJ(POCHB) = 10-5 Hz but on increasing the concentration of nickel acetylacetonate in solution first... 

The same features exist at a reduced level for POCCH couplings in phosphorinanes and these are about 2-6 Hz for an equatorial proton at C-5, while it is less than 1 Hz for an axial proton. Similarly, coupling of phosphorus to an equatorial methyl at C-4 is 2 to 3 Hz while that to axial methyl is less than 1 Hz (1968>83) similar trends have been found in the corresponding phosphonates.<1969,52)... 

Another system, which is also allowed by IUPAC and is sometimes very convenient (but which should be avoided when official names are established by IUPAC and cited in Chemical Abstracts), is the so-called a -nomenclature, in which the term phospha indicates replacement of carbon by phosphorus, e.g. phosphacyclohexane = phosphorinane, and phosphabenzene = A3- phosphorin. Five-coordinate phosphorus compounds are called phos-phoranes. However, this name is also used for phosphorus ylides with a four-coordinate phosphorus and a more or less polar R3f—CX moiety or a d -p R3P=CX double bond, e.g. methylenetriphenylphosphorane = triphenylphosphorus methylene ylide or tri-phenylphosphonium methyl ylide, Ph3P=CH2 = Ph3P—CH2. 

Phosphorinanes (1), R being H, alkyl, aryl, halogen, OR, NR2 and others, are known. Like open chained P compounds of CN = 3, most of these compounds are air sensitive and non-crystalline. The six-membered ring is nearly always in a chair conformation. Both structures (la) and (lb) are possible, R being axial (a) or equatorial (e). 

Three main types of reaction are used to convert the phosphorinanes (P-GV = 3) into phosphorinanes (P-CN = 4) alkylation, oxidation and sulfuration. 

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