Cyclopenta pyran derivative

Recently reported rearrangements of linear triquinanes (244) to their angularly fused isomers (247) have been envisaged to involve the formation and equilibration of the enolates (245) and (246) followed by an intramolecular Michael addition of the enolate ion in (246) to the cyclopentenone moiety see Scheme 62. It has been reported that treatment of l,10-dibromobicyclo[8.1.0]undecane-3,8-dione (248) with triethylamine in dichloromethane results in the formation of a novel cyclopenta[(>]pyran derivative (249). The mechanism outlined in Scheme 63 has been postulated to account for this unusual transformation. 

The cyclopenta[c]pyran system 6 is formed when allenyl propynyl ethers are heated in CO in the presence of Co/Rh nanoparticles a Pauson-Khand reaction is involved <07SL453>. An enantioselective Bronsted acid-catalysed Nazarov cyclisation of a dihydropyran-based divinylketone affords cyclopenta[/>]pyrans 7 <07AG(E)2097> and Sc and In triflates catalyse a similar reaction of 6-alkenoyl derivatives of both dihydropyran and thiopyran <07S1733>. 

Fischer-type chromium carbene complexes with 1-ethoxycyclopropylalkynyl substituents at the carbene carbon, e.g. 25, on reaction with dimethylamine and subsequent conversion of the resulting vinylcarbene with alkynes surprisingly did not give phenol derivatives, as would be expected from the known Dotz reaction, but gave cyclopenta[ )]pyrans, e.g. 26. The reaction is interpreted as a double alkyne-insertion/CO-insertion sequence with formation of a trienylketene intermediate, which undergoes intramolecular hetero-Diels-Alder cycloaddition and dimethylamine elimination. ... 

Hong reported an unexpected formation of a cyclopenta[c]pyran derivative 173 by the [6+3]-cycloaddition of 6-dimethylaminofulvene 109 andp-benzoquinone 174 (Scheme 6.44a) usually, fulvenes react with 174 to give [4+2] cycloadducts... 

As mentioned in Chapter 7, soon afterwards, Hong reported another unexpected formation of cyclopenta[c]pyran derivative 317 by a [6-h3] cycloaddition of dimethylaminofulvene 109 and />-benzoquinone 174 [108]. He developed a solid-phase synthesis of 317 and cyclopenta[c]quinolone derivatives 318 using a resin-bonded fulvene derivative and a hetero [6+3] cycloaddition sequence (Scheme 6.78) [101]. 

Many interesting photochemical reactions are possible with pyran-2-one and its various alkyl and benzo derivatives. For example, irradiation of 2-oxo-2/7-l-benzopyran 4-carbonitrile 170 in the presence of excess 2,3-dimethylbut-3-ene in Ar-degassed benzene provided imino-substituted cyclopenta[c]annelated product 171 (Scheme 19)... 

These are (1) The chiral substrate approach. This approach involves using chiral precursors that transfer their chirality to the final cyclopentenone. This implies the synthesis of chiral substrates, which has generally been made from classic chiral pools. Examples include carbohydrate derivatives like 40 that give 41 with variable yields depending on the substitution pattern. 41 is transformed into cyclopenta[c]pyrane 42, which is the skeleton of iri-doids [93]. In another example epichlorhydrin (43) is used to construct chiral enyne 44 which gives cyclopentenone 45 [94] (Scheme 14). 

For the preparation of the benzo[i>]cyclopropa[d]pyran 2-599, Ohta and coworkers have treated 3-ethoxycarbonylcoumarin (2-597) with dimethylsulfoxonium methylide (2-598), derived from the corresponding trimethylsulfoxonium iodide and NaH (Scheme 2.136) [307]. The isolated product was not 2-599, however, but an unexpected cyclopenta[i>]benzofuran derivative 2-600 probably formed through 2-599. 

A Nazarov cyclisation of l-(3,4-dihydro-2//-pyran-6-yl)-3-phenylpropenones affords cyclopenta[Z)]pyranones (Scheme 9) <03OL4931> and the conjugated ethoxytriene 7 derived from tetrahydropyran-2-one also yields a fused cyclopentenone <03JOC9728>. 

Sato, M., Takayama, K., Sekiguchi, K., Abe, Y., Furuya, T., inukai, N., Kaneko, C. Synthesis of opticaiiy active cyclopenta[c]pyran-4-carboxyiic acid derivatives, buiiding biocks for iridoids. An attractive aiternative to the asymmetric de Mayo reaction. Chem. Lett. 1989, 1925-1928. 

Participation in [2-t-l] cycloaddition to form cyclopropane derivatives Diels-Alder Cycloaddition 1,3-Dipolar Cycloadditiorv [3h-2h-1] cycloaddition (i.e., theDdtzBen-zamulation to form functionalized phenol derivatives " ), [3-i-2-i-2-i-l] cycloaddition to give cyclopenta[Z ]-pyrans and [3-i-1h-1], [3h-2h-2], [3-i-2-i-2-i-2], and [4-i-l] cycloaddition. ... 

The reaction of 1,2-diphenylethanedione with the CP anion unexpectedly affords a novel 2,3,7-triphenyl derivative of the bicyclic cyclopenta[c]pyran 311, which has a planar structure and relatively large bond alternation (Scheme 6.76a) [182]. Babaev reported that oxazolo[l,2- ]pyridinium salts 312 react with CP anion, leading to cyclopenta[ ]quinolizines 313. Parent pyrindines 250 (X = NR) are... 

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