Clemmensen reduction of 2-acetylfluorene. Pathways for the formation of 2,3-di(2-fluorenyl)butane and its homologues

Abstract

The Clemmensen reduction of 2-acetylfluorene gave not only 2-ethylfluorene but also 2-(a-hydroxyethyl)fluorene, 2-vinylfluorene, cis-and trans-2,3-di(2-fluorenyl)-2-butene, meso-and dl-2,3-di(2-fluorenyl)butane, 2,3-di(2.fluorenyl)-2,3-butanediol, 3,3-di(2-fluorenyl)-2-butanone, and 3,3-di(2-fluorenyl)-2-butanol. The confirmation of these compounds was achieved by established syntheses. The Clemmensen reduction of 2-acetylfluorene may proceed through the corresponding carbinol, 2-(a-hydroxyethyl)fluorene, to the normal reduction product, 2-ethylfluorene.The Clemmensen reduction of 2-acetylfluorene ( 1)112 has been reported by Campbell and Wang3 to yield only 2-ethylfluorene (2)4-6 in 45% yield.The present paper deals with the reinvestigation of this reduction and 1 was found to form not only 2 (76%) but also intermediary compounds, 2-(a-hydroxyethyl)fluorene (3)7 and 2-vinylfluorene (4),6-8 and the related dimeric products, namely 2,3-di(2-fluorenyl)-2,3-butanediol ( 5 ) , 3,3-di(2-fluoreny1)-2-butanane (6), 3,3-di(2-fluorenyl)-Z-butanol (7), cis-(Sa) and trans-2,3-di(2-fluorenyl)-2-butene (Sb), and meso-(9a) and dl-2,3-di(2-fluorenyl)butane (9b). The structural proof for these compounds was confirmed by authorized syntheses.Scheme I 1 2 3 4 5 8 0These results suggest, on the grounds of the formation of intermediaries 3 and 4, t h a t the reduction sequence of 1 may differ somewhat from the conventional concept of the Clemmensen r e d u c t i~n ;~ generally, the reaction cannot proceed through the corresponding carbinol since the carbinol itself is not reduced.The reduction of 1 gave, in addition to 2, a pair of cis, trans isomers, Sa and Sb, and diastereomers of 9a and 9b. The formation of these isomers provides some interesting stereochemical information, because the recent studies of the Clemmensen reduction have rarely observed such abnormal products as these stereoisomers. Sequence of the Formation of 2-Ethylfluorene (2) by the Clemmensen Reduction of 2-Acetylfluorene (1).The reduction of 1 and its homologues was carried out in xylene using amalgamated zinc and hydrochloric acid according to t h e method described in Organic reaction^.^ These results are summarized in Table I.At an initial stage of the reduction, 1 yielded 2,3,4,5,6,9a, and 9b. Carbinol 3 was also reduced to 2 accompanied by small amounts of 9a and 9b as easily as in the case of 1. The Clemmensen reduction of olefin 4 afforded 2, but the yield of 2 was smaller than t h a t from 1. Additionally, the deuteriocarbinol, 2-(a-hydroxyethyl)fluorene-C,,0-dz, was converted into 2-ethylfluorene-C,-d and meso-and dl-2,3-di(2-fluorenyl)butane-Cz,C3-d~ under similar reaction conditions, as Scheme I1 shows. Scheme I1@&-=FI -These findings are explained by assuming that the carbinol 3 is one of the important intermediates in the Clemmensen reduction of 1. T h e sequence of the formation of 2,3,4, and 9 is presumed as Scheme 111. Carbinol 3 may be formed from Scheme I11 , OH . Fl-C;CH3___) iF1-A-CI13

A new preparative method for .alpha.,.beta.-unsaturated .delta.-lactones from the reaction of 3-hydroxy acids with 1,3,5-trioxane

“…A mixture of 9 (0.25 g, 1.1 mmol) and P2O5 (0.50 g) in xylene (20 mL) was refluxed for 2 h to give 0.22 g (95%) of 2, which was identical in all respects with an authentic specimen.…”

“…2.3 (t, J = 6 Hz, 2 H, CH3CH2CH2), 2.7 (m, 1 H, -CHC=C).3.6-4.4 (m, 2 H, d, J = 7 Hz, 6 H, (CHskCH],1.4-2.1 [m,8H,-(CH2)4-],2.and 1.1 (d, J = 6 Hz, 6 H, CH3CH 2X), 1.4-1.85 [m, 10 H, -(CH2)5-]. 2.0 (m, 1 H, (CH3)2-CH-), 2.2 (d, J =9 Hz, 1 H, -CHCOO-),5.3 (q, JAB = 6 (t, J = 6 Hz, 3 H, CH3CH2), 1.2-1.9 [m. 16 H,-(CH2)5-, -(CH2)3-],2.45 (d, J = 9 Hz, 1 H, -CHCOO-),5.3 (q, JAB = 6 Hz, 2 H, -OCHC-) Ig 27925Is, 6 H, fCH3)2], 1.3-1.8 [m. 10H,-(CH2)s-],5.3(s,2H, -och2o-> °acidii mmol), 1,3,5-trioxane (30 mmol), 97% sulfuric acid (2.5 g), and acetic acid (50 mmol) were used; reaction time, 8 h. The yields are based on 3-hydroxy acid. c Paraformaldehyde was used instead of 1,3,5-trioxane.…”