Preparation of Oligopyrrole Macrocycles Precursors
1127
reason s, but also as water is a un ique solven t (polarity, dielectric con stan t,
specific H-bon din g, etc.). Th ere is, of course, on e severe lim itation to th e
use water as a m edium for organ ic reaction s, wh ich is lim ited water solubil-
ity of th e m ost organ ic com poun ds. Alth ough , th e ch em istry of today
kn ows th at reaction s can take place even in th e solid state, th e n ecessity of
liquid m edium for m ost organ ic reaction s rem ain s. It is gen erally accepted
th at everyth in g is soluble in everyth in g, an d th e question is on ly, h ow
m uch . Th e low reagen t con cen tration s results in th e low reaction rates,
wh ich is th e m ain lim itation s of water as reaction solven t. Th e con cen tra-
tion of reagen ts can be en h an ced by addin g of usually ion ic organ ic com -
poun ds for form ation of m icelles, or dissolvin g organ ic m olecules in water
usin g, e.g., cyclodextrin in clusion com plex form ation , or just addin g som e
polar organ ic com poun ds soluble in water like alcoh ols.
Th e water m edium h as been already successfully used e.g. for syn th esis of
th e lowest h om ologs of tetraalkylm esoporph yrin 1, Mich ael addition s2,3
,
zin c m etal-m ediated ch em oselective reduction of n itroaren es4, reduction
of arom atic rin gs usin g a Ran ey Ni-Al alloy5, dech lorin ation of ch lorobiph e-
n yls6, or even a Grign ard-like reaction 7.
Our group is in terested in ch em istry of oligopyrrole m acrocycles, wh ich
h as developed with in th e last decade, goin g from classic porph yrin an a-
logues to con tracted an d expan ded porph yrin oids as well as to system s
with stopped or fully rem oved con jugation 8. Sim ple syn th etic m eth odology
was sufficien t for preparation of sym m etrical porph yrin derivatives, wh ere
th e m ost popular9 becam e Roth em un d an d Adler-Lon go 4×1 approach es. By
th is m eth odology, Japan ese auth ors recen tly reported preparation of con -
jugated h igh er oligopyrrole m acrocycles, wh en pen tafluoroben zaldeh yde or
2,6-dich loroben zaldeh yde was used10. We h ave recen tly reported also a
great poten tial of oligopyrrole m acrocycles for an alytical11 as well as m edic-
in al12 application s an d m olecular recogn ition 13. But n ow, with n ew devel-
opm en t in th e area of in verted (con fused)10, expan ded porph yrin s8,14, th ere
is a great n eed for sim ple an d reliable syn th esis of con ven ien t buildin g
blocks for th e n ovel oligopyrrole m acrocycles. In oth er words, th e furth er
developm en t in th is area depen ds on availability of buildin g blocks, m ain ly
for lin ear oligopyrrole system s, dipyrrom eth an es 3 an d tripyrrom eth an es 4.
In spite of relative sim plicity, a gen eral, reliable an d sim ple m eth od for
th e preparation of lin ear oligopyrroles rem ain s a ch allen ge. Even sim ple
m olecules like dipyrrom eth an es 3 with β-un substituted pyrrole h ave been
reported by Lin dsey on ly a couple of years ago by reaction of aldeh ydes
with excess of pyrrole. Dipyrrom eth an es with β-substituted pyrrole are usu-
ally prepared by m ultistep syn th esis, based on form ation 5,5′-bis esters of
Collect. Czech. Chem. Commun. (Vol. 69) (2004)