Tracy Massil

Cycloaddition of Bu3P·CS2: Formation of extended bis- and tris-1,3-dithiolanes and dithiolane-containing polymers

Abstract Reaction of the tri-n-butylphosphine/carbon disulfide adduct 1 with norbornene and aromatic di- and trialdehydes gives the bis- and tris-dithiolanes 7–9 resulting from Wittig reaction of 2. In the same reaction, norbornadiene diester 10 reacts only on the unsubstituted double bond to give bis-dithiolanes 11 and 12, while norbornadiene itself reacts on both double bonds to give novel dithiolane-containing polymers 13–15. In the bis-dithiolane 16 derived from reaction of 1, norbornene and phthalaldehyde, the groups interact leading to cyclisation so that only the spiroindane isomer 17 is obtained and its X-ray crystal structure is presented. In the reaction of 1, 10 and phthalaldehyde the initial product 21 can be observed but it similarly cyclises upon acid catalysis to afford 22. By treatment of 21 with HBF4 followed by Et3N the opposite stereoisomer 23 is mainly obtained in addition to 22.

CYCLOADDITION OF BUN3P.CS2 : DIRECT ONE-POT CONVERSION OF STRAINED DOUBLE BONDS TO 2-ALKYLIDENE-1,3-DITHIOLANES

Abstract Reaction of the adduct between tri-n-butylphosphine and carbon disulfide 1 with norbornene gives the novel zwitterionic structure 9. In solution this dissociates to the ylide 8 which undergoes Wittig reaction with aldehydes. Using the same method, the overall conversion of the strained double bond in a variety of bicyclo[2.2.1]alkenes into 2-benzylidene-1,3-dithioles 15–24 has been achieved and the reaction is also applicable to norbornadiene, affording bis-dithiolanes 29–31.

Preparation of heterocyclic phosphorus ylides containing the tetramic acid ring system and seven-membered ring vinylogues

Abstract Pyrolysis of amino acid-derived (α-aminoacyl)(ethoxycarbonyl)ylides results in ring closure with extrusion of ethanol to give novel five-, six- and seven-membered ring heterocyclic ylides.

Cycloaddition of Bun3P·CS2: direct one-pot conversion of strained double bonds to 2-alkylidene-1,3-dithiolanes

Reaction of the strained double bond in bicyclo[2.2.1]heptene systems with Bun3P·CS2 and an aldehyde provides convenient access to the corresponding 2-alkylidene-1,3-dithiolanes.

Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 17. Preparation of aliphatic amino acid derived γ-alkoxycarbonylamino-β-oxo ylides and pyrolysis to give α,β-acetylenic γ-amino acid and GABA analogues

A series of eleven α-aminoacyl stabilised phosphorus ylides 9–19 have been prepared by condensation of N-alkoxycarbonyl protected amino acids with Ph3PCHCO2Et using a carbodiimide peptide coupling reagent. Upon flash vacuum pyrolysis at 600 °C, these undergo extrusion of Ph3PO to give the corresponding α,β-acetylenic γ-amino esters 21–29, 33 and 34 in moderate yield. In two cases the terminal alkynes 30 and 31 are also formed. The β-aminoacyl ylide 20 from β-alanine similarly gives the α,β-acetylenic δ-amino ester 35 upon pyrolysis. Regioselective addition of HBr to the triple bond of one acetylenic ester 25 was observed giving a mixture of E and Z α-bromoacrylates 36. Hydrogenation of the N-Cbz acetylenic esters 21–23 and 33 results in N-deprotection and hydrogenation of the triple bond to afford the chiral GABA analogues 37–40 in 70 –>95% ee as determined by 19F NMR of their Mosher amides. Fully assigned 13C NMR spectra of all the ylides and acetylenic ester derivatives are presented.

Pyrolysis of Cyclic Polyoxo Phosphorus Ylides

In an extension of our recent work on generating acetylenic amino acid derivatives by flash vacuum pyrolysis (FVP) of appropriate stabilised phosphorus ylides,1 we examined the ylides 1 with a free amino group. Rather than the expected acetylenic product these gave the novel cyclic ylides 2 with loss of ethanol. Preliminary attempts to bring about extrusion of Ph3PO from these gave rather confusing results so we have examined simpler cyclic ylides in an attempt to understand the processes involved.

Synthesis of Amino Acid Derived Cyclic Phosphorus Ylides

Abstract We recently reported the thermal elimination of Ph3PO from suitably protected aminoacyl ylides 1 as a route to acetylenic amino acid analogues 2. Pyrolysis of ylides such as 3 with a free amino group takes a different course. Ethanol is eliminated to give the c h i d cyclic ylides 4 which can be viewed as 3-triphenylphosphoranylidene tetramic acids. Specific examples prepared include 4 (R = Me, Pri), the parent compound 5 (from glycine) and the six-membered ring compound 6 (from p-alanine). Using a similar approach, bicyclic ylides such as 7 (from proline) can be prepared. In the case of the glutamate derived ylide 8, thermolysis initially gives a mixturc of 9 and 10 but these both cyclise to the bicyclic product 11 with time. The structure and reactivity of these interesting cyclic ylides are now being examined.