Sumwary The 13C-31P coupling constant is ca. 30 Hz for a trans 2-Me group in a 1-substituted AS-phospholene and is negligible in the cis-isomer; the corresponding isomeric oxides show no appreciable differences in 2Jpcc.3 Preparations and stereochemical assignments were similar to procedures used previously.'

l-Methyl-3-phospholanol (cis, trans) has been prepared by reduction of 1 -methyl-3-phospholanone with several agents, preferably lithium aluminum hydride, as well as by P-deoxygenation of the alcohol mixture formed on catalytic hydrogenation of l-methyl-3-phospholanone 1-oxide. The phospholanol mixture is easily analyzed by the well-separated (13 Hz) PCH3 nmr signals; the downfield signal is attributed to the cis isomer, which predominated (84%) from the various reductions of the phospholanone. The route via the phospholanone oxide gave predominantly the trans alcohol (63%). The conformational equilibrium for the cis isomer appears to be dominated by the diaxial conformer. Addition of methylmagnesium iodide to the phospholanone follows a similar steric path, and gives mostly the cis isomer.

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When heated at 140-150°for 3.5 hr, 13.6 g of 5 and 60.1 g of DEHP yielded 3.04 g (11.1%) of crude product which had a composition similar to the run with the peroxide.Hydrogenation of the Limonene Adducts. A 0.3 g sample of 10 was reduced in 10 ml of acetic acid using 29.5 mg of Pt02 as catalyst. The sample absorbed only 2.45 ml (STP 13% of theory) of H2 in 42 min. Glc of the 0.29 g recovered indicated that it was mostly starting material.A 0.16 g sample of 11 and 26.2 MgPt02 in 5 ml of acetic acid absorbed 12.84 ml (STP, 98% of theory) of H2 in 44 min. Glc of the recovered material (0.15 g, [a]25o 0°(15% EtOH)) showed a peak at a (11) 0.731. Ir bands at 1250-970 cm-1 indicated the presence of the phosphonate structure.

Abstract-The 13C-31P coupling constant is much larger for a 2-methyl substituent (about 20 Hz) than for a 3-methyl substituent (about 5 Hz) in phospholes and 2-phospholenes, and appears useful for assigning structures in these compounds.IN THE interpretation of the NMR spectrum of I-methylphosphole,l we proposed that 31P coupling with the proton at the 2-position [2J(P-H)] was more extensive (38-5 us. 13.8 Hz) than with the 3-pr0ton[~J(P-H)]. Although this view was the opposite of that commonly held for P-H coupling in phosphines, it has been fully substantiated in later work2 and also found applicable to the 2-phospholene ~y s t e m .~ In the course of an examination of the I3C NMR properties of phospholes and phospholenes, we have discovered that the same relation is true for 31P coupling with 13C of methyls attached to sp2 carbon; 2J(P-C) is considerably larger than 3J(P-C). This specificity is unusual, for in acyclic phosphines 2J(P-C) and 3J(P-C) (as well as 'J(P-C)) are of similar magnitude and little structural information