α,β-functionalization of enones via pentacovalent oxaphospholenes

[4 + 2] Cycloadditions of 1-phosphono-1,3-butadienes with nitroso heterodienophiles: a versatile synthetic route for polyfunctionalized aminophosphonic derivatives

The hetero-Diels-Alder (HDA) reaction of 1-(diethoxyphosphonyl)-1,3-butadiene, 1-(dibenzyloxyphosphonyl)-1,3-butadiene, and 1-(diethoxyphosphonyl)-3-tert-butyldimethylsilyloxy-1,3-butadiene with various nitroso heterodienophiles has been investigated as a new synthetic route for aminophosphonic derivatives. The HDA cycloadditions regioselectively led to the proximal isomers, i.e., presenting the NR(3) group in the meta position regarding the phosphonate substituent. From the resulting 6-phosphono-3,6-dihydro-1,2-oxazine cycloadducts, a limited number of chemical steps were allowed to obtain a significant variety of aminophosphonic compounds of potential interest in medicinal chemistry. This has been illustrated through the synthesis of (Z)-4-(o-tolylamino)-1-hydroxybut-2-enylphosphonic acid, diethyl 3,4-dihydroxy-1-o-tolylpyrrolidin-2-yl-2-phosphonate, 4-(o-tolylamino)-1,2,3-trihydroxybutylphosphonic acid, diethyl 3-(2-(o-tolylamino)-1-hydroxyethyl)oxiran-2-yl-2-phosphonate, and diethyl 4,5-dihydroxymorpholin-6-yl-6-phosphonate.

Selective preparation of (E)-3-oxo-1-alkenylphosphonates by insertion of acyl chlorides and nitriles into zirconacycles

Zirconacycles 1, obtained from diethyl 1-alkynylphosphonates, insert either acyl chlorides or nitriles to provide, after acidic workup, (E)-3-oxo-1-alkenylphosphonates, 2, in isolated yields of 55-83%. Insertion produces only one regio- and stereoisomer. The reaction is quite general and proceeds well with both aliphatic and aromatic acyl chlorides. Acetonitrile and p-methoxybenzonitrile also inserted efficiently. Insertion of isobutyl chloroformate produced the vinylphosphonocarboxylate, 2c, the first representative of this class of compounds.

Zinc-mediated chain extension of beta-keto phosphonates

A variety of beta-keto phosphonates can be converted to gamma-keto phosphonates through reaction with ethyl(iodomethyl)zinc. The presence of alpha-alkyl substituents, Lewis basic functionality, and modestly acidic NH-protons are accommodated in substrates of this reaction. Chain extension of beta-keto phosphonates that contained olefinic functionality proceeded more quickly than cyclopropanation; however, it was not possible to effect the chain extension to the exclusion of cyclopropane formation. A primary reason for this imperfect chemoselectivity appears to be the slow chain extension of beta-keto phosphonates. Nevertheless, the simplicity, the scope, and efficiency of this method serve to make it an attractive alternative to the established methods for gamma-keto phosphonate formation.

Synthetic Studies toward the Preparation of Phosphonate Analogs of Sphingomyelin and Ceramide 1-Phosphate Using Pentacovalent Organophospholene Methodology

Model studies for the syntheses of phosphonate analogs of sphingomyelin and ceramide 1-phosphate are described. The pentacovalent oxaphospholene 3b (derived from methyl vinyl ketone and triethyl phosphite) readily condensed with dialkyl azodicarboxylates (R = Et, t-Bu, CH(2)CCl(3)) to form beta-hydrazido gamma-ketophosphonates 5 and 8 in excellent yields. Cleavage of the N-N bond in 5a (R = Et) or 5b (R = t-Bu) via standard methods was unsuccessful. Upon reduction with NaBH(4), 8 produced the oxazolidinone 9 (93%) as a diastereomeric mixture of 3:1. Treatment of 9 with Zn/HOAc/acetone at rt readily cleaved the N-N bond to form 11 (78-83%). Confirmation of stereochemical assignments in 11 (3:1, trans:cis) was accomplished via NOE experiments.