Fluorene, 9- cycloaddition reactions

The 1,3-dipolar cycloaddition reaction of azomethine ylides with thioketones has been used to prepare 1,3-thiazoIidines. The metallated azomethine ylides 67 were generated in situ by treating a-amino acid ester imines 66 with lithium bromide and DBU. The ylides were then treated with highly reactive thioketones such as thiobenzophenone or fluorene-9-thione, to afford 1,3-thiazolidine derivatives 68 (main isomer) and 69 (minor isomer) in good yield and in diastereoisomeric ratios of between 2 1 and 4 1 <01H(55)691>. 

The formal 2 -I- 2-cycloaddition reaction of platinum(ll) acetilides (14) with TCNE and TCNQ initially produced 7,7,8,8-tetracyano-p-quinodimethane cyclobuta-1, 3-dienes that undergo retroelectrocyclization to produce feis-cycloadducts (15, 16). In all examples investigated, the triple bond adjacent to the platinum atom did not react with the TCNE or the TCNQ (Scheme 5). The 2-I-2-cycloaddition of substituted cyclobutadiene-AlCl3 complexes (18) with methyl phenylpropynoate (17) produced Dewar benzene intermediates (19) that readily converted to 1,2,3,4-tetramethyl- and 1,2,3,4-tetraethyl-fluorenes (20) (Scheme 6). The first rhodium-catalysed inter-molecular 2-1-2-cycloaddition of terminal alkynes with e-deflcient alkenes yielded substituted cyclobutenes in high yields (99%) and complete regioselectivity. An 8-quinolinolatorhodium/phosphine catalyst (21) was employed in this reaction. ... 

The reactions between benzotriafulvenes and transition metals (Pt and Rh) afford metallacyclobutane derivatives 41 as stable crystalline compounds in good yields. Recently, Huang developed the highly regioselective palladium-catalyzed [i+2] cycloaddition reactions of 34 (R = Ph) with arynes or alkynes to provide fluorene 42 and rndene derivatives 43, respectively (Scheme 6.4) [24]. 

Intramolecular [4+2] cycloaddition reactions of conjugated enynes, namely, dehydro-Diels-Alder reactions, afford benzo-fused CPDNs [254]. Thus, 2-propynyldiarylacetylenes 413 undergo thermal intramolecular [4+2] cycloadditions to give benzo[fc]fluorene derivatives 414 in good yields (Scheme 6.108a). The reactivity of the reactions increases in the order hydrocarbon... 

Au(I)/complex-catalysed formal intramolecular 3 + 3-cycloaddition reaction of 0-alkynylstyrenes (125) generated 6,6a-dihydro-5//-benzo[fl]fluorenes (126), which could be converted to 6,1 l-dihydro-5//-benzo[fl]fluorenes (Scheme 39). °... 

Treatment of the propargylic alcohol 144, readily prepared from condensation between benzophenone (143) and the lithium acetylide 101, with thionyl chloride promoted a sequence of reactions with an initial formation of the chlorosulfite 145 followed by an SNi reaction to produce in situ the chlorinated and the benzannulated enyne-allene 146 (Scheme 20.30) [62], A spontaneous Schmittel cyclization then generated the biradical 147, which in turn underwent a radical-radical coupling to form the formal [4+ 2]-cycloaddition product 148 and subsequently, after a prototropic rearrangement, 149. The chloride 149 is prone to hydrolysis to give the corresponding 11 H-bcnzo h fluoren-ll-ol 150 in 85% overall yield from 144. Several other llff-benzo[fc]fluoren-ll-ols were likewise synthesized from benzophenone derivatives. 

A novel protocol for the synthesis of new dispiro-pyrrolo/pyrrolizidino ring systems has been achieved by the [3+2] cycloaddition of azomethine with dipolaro-phile 9-arylidine-fluorene (Jayashankaran et al., 2004). They have reported superior yield and high rate of reaction by this solvent-free microwave-assisted approach. 

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