Regioselective Synthesis of Trisubstituted Cyclopentadienyl Ligands from Furans

Abstract

1,2,3-And 1,2,4-trisubstituted cyclopentadienyl manganese tricarbonyl compounds have been synthesized regioselectively from furans following a common synthetic strategy. The key steps include the transformation of furylcarbinols into hydroxycyclopentenones followed by the conjugate addition of Grignard reagents under chelation directed conditions. This affords hydroxycyclopentanones which can be dehydrated to cyclopentenones. These compounds are further elaborated into the final targets by the 1,2addition of organolithium reagents.

Enantioselective preparation of (R) and (S)-3-hydroxycyclopentanone by kinetic resolution

“…This corresponds to an E = 20. This is in line with the earlier observation that only cyclopentanol derivatives with large or many substituents give high E value in kinetic resolution [21][22][23][24][25][26][27][28][29][30][31][32][33]. Those with small and few substituents, such as cyclopent-4-ene-1,3-diyl diacetate (80% yield, 20.5% ee) [34], cyclohex-2-en-1-yl acetate [35], 4-hydroxycyclopent-2-en-1-one (E = 11) [36], 4-hydroxy-2-methyl-2-cyclopentenone (60% yield, 60% ee) [37], 3-bromocyclopent-2-enol [38] give less enantiopure products.…”

“…A general trend observed is that derivatives with large substituents are readily resolved [21][22][23][24][25][26][27][28][29][30][31][32][33], while simple compounds similar to our target molecule tend to give low E values [34][35][36][37][38].…”

Synthetic Study of 1,3-Butadiene-Based IMDA Approach to Construct a [5−7−6] Tricyclic Core and Its Application to the Total Synthesis of C8-epi-Guanacastepene O

“…To this end, we needed to make compound 26 (Scheme ). Accordingly, furan 24 was first treated with ZnCl 2 in dioxane−H 2 O as a cosolvent to give a cyclopentenone, which then underwent 1,2-addition of MeLi to afford 25 in 68% yield for two steps. The secondary alcohol in 25 was first protected as the TBS ether and then transferred to the key intermediate 26 by PCC-mediated oxidative rearrangement …”

Stereocontrolled synthesis of highly functionalised spirocyclic pyrans

“…The synthesis of the [4.5]decadiene cyclisation precursor began with 2-lithiofuran which was trapped with isobutyraldehyde to generate furfuryl alcohol 15. 15 Protection of the resulting hydroxy group as the corresponding TBS ether followed by C 5 allylation then generated alkene 16, which upon deprotection afforded the desired precursor 19 (Scheme 6). For the synthesis of the [5.5]undecadiene and the [5.7]tridecadiene precursors, however, 2-lithiofuran was alkylated with 4bromo-1-butene and 6-bromo-1-hexene respectively to generate the 2-alkenyl units 17 and 18.…”