Phosphites ring closures with

Stereospecific ring closure. 2/ -Azido-3a-iodocholestane in benzene added to tri-methyl phosphite, allowed to stand at room temp, until spectroscopy shows disappearance of the IR-azide band, solvent and most of the excess trimethyl phosphite removed in vacuo, the ethereal soln. of the residue added to a stirred soln. of LiAlH4 in anhydrous ether at a rate to maintain reflux, and stirred 2 hrs. at room temp. 2, 3i -iminocholestane. Y 16%. - This convenient reaction sequence may be successful in cases where other methods fail. F. e., also isolation of the intermediate, and ring closure with other phosphorus(III) nucleophiles such as phosphines, s. A. Hassner and J. E. Galle, Am. Soc. 92, 3733 (1970). 

More recently, a double reductive ring closure of the dinitrodiphenylbenzene 139 with triethyl phosphite as the reducing agent has been reported to produce 3 in 59% yield (Scheme 18). The precursor 139 was prepared in excellent yield by Pd(0)-catalyzed coupHng of phenylboronic acid and 1,3-dibromo-4,6-dinitro-benzene (92JHC1237). 

A variety of pyrrole ring closure reactions are conveniently formulated as proceeding via nitrene intermediates, although it is doubtful whether a free nitrene is involved. Pyrolysis of o-nitrobiphenyls with iron(II) oxalate (61T(16)80), or reduction under milder conditions with triethyl phosphite (65JCS4831) or tris(trimethylsilyl) phosphite (79TL375), leads to the carbazole, as does the pyrolysis or photolysis of 2-azidobiphenyls (Scheme 3) (75JA6193). 

The disulfide-enols 345 were converted to oxazoline-azetidinones 346 by intramolecular trapping of the azetinium cation [or of an intermediate 5-epiclavem 196] by the acylamino oxygen atom (various protocols trimethyl phosphite or triphenyl-phosphine treatment preferred). After mesylation, oxaz-oline cleavage with dry HCl afforded chloroazetidinones 347 with neat inversion of configuration, which underwent ring closure (H2S/TEA) to give the prescribed (5 R )-6-acylamino-2-methylpenems. 

Two reports describe the first analogues to cyclic carbohydrates having phosphorus at the anomerlc centre ("phostones ). Puranoid analogues (11) and (12) were obtained by hydrolysis of the phosphite (13) together with the acyclic product (li ) (Scheme 2), the latter undergoing ring closure to (11) and (12) on treatment... 

A soln. of 5-methyl-9-octalin-2-one in abs. methanol-methylene diloride cooled at Dry Ice-acetone bath temp, treated 52 min. with a Og-O -stream until the soln. becomes blue from excess Og, purged with Ng, trimethyl phosphite added, and stirred 19 hrs. at room temp. -> 2-methylbicyclo[5.3.0]dec-l(7)-ene-6,8-dione. Y 80%. - Spontaneous transannular ring closure of the presumed intermediate occurs. F. e. s. R. A. Kretdimer and W. M. Sdiafer, J. Org. Chem. 38, 95 (1973). 

---