Synlett 2015; 26(15): 2121-2126
DOI: 10.1055/s-0035-1560052
letter
© Georg Thieme Verlag Stuttgart · New York

Zinc-Mediated Allylation Followed by Lactonization of Dialkyl 2-(3-Oxo-1,3-diarylpropyl)malonates: Construction of δ-Lactones with Multiple Stereocenters

Chennakesava Reddy
Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali, Manauli P.O., Punjab, 140306, India   Email: sababu@iisermohali.ac.in
,
Srinivasarao Arulananda Babu*
Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali, Manauli P.O., Punjab, 140306, India   Email: sababu@iisermohali.ac.in
› Author Affiliations
Further Information

Publication History

Received: 29 May 2015

Accepted after revision: 02 July 2015

Publication Date:
20 August 2015 (online)


Abstract

A variety of polysubstituted δ-lactones containing three or four stereocenters were prepared from various dialkyl 2-(3-oxo-1,3-diarylpropyl)malonates by a Barbier-type zinc-mediated allylation or cyclohexenylation of the keto group, followed by intramolecular lactonization/transesterification. The stereochemistry of the major isomers was confirmed by X-ray crystal structure analysis of representative compounds.

Supporting Information

 
  • References and Notes

  • 8 Crystallographic data for compounds 3b, 3c, 3t, and 4b have been deposited with the accession numbers CCDC 1048540, 1048541, 1048542, and 1048543, respectively, and can be obtained free of charge from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44(1223)336033; E-mail: deposit@ccdc.cam.ac.uk; Web site: www.ccdc.cam.ac.uk/conts/retrieving.html.
  • 9 γ-Lactones 3su and δ-Lactones 3ar and 4ah; General Procedure Zn powder (0.37 mmol) and allylbromide or 3-bromocyclohexene (0.5 mmol) were added to a solution of the appropriate malonate substrate 1 (0.25 mmol) in anhyd THF (1.5 mL) under N2, and the mixture was stirred at 30–35 °C for the appropriate time (see Table 1 and Schemes 2–4). The reaction was then quenched by adding H2O (2 mL), and the mixture was allowed to stand. The mixture was transferred to a separatory funnel and extracted with EtOAc (3 × 8 mL), and the organic layers were combined, dried (Na2SO4), filtered, and concentrated under vacuum. The resulting crude product was purified by column chromatography (silica gel, EtOAc–hexane). Ethyl (3S*,4S*,6S*)-6-Allyl-4-(4-chlorophenyl)-2-oxo-6-phenyltetrahydro-2H-pyran-3-carboxylate (3b) Prepared by the general procedure from 1b, and purified by column chromatography [silica gel, EtOAc–hexanes (13: 87)] as a colorless solid (major isomer); yield: 97 mg (98%; dr 75:25); mp 87–89 °C. IR (KBr): 1747, 1726, 1494 and 1155 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.41–7.28 (m, 5 H), 7.32 (d, J = 8.4 Hz, 2 H), 7.13 (d, J = 8.4 Hz, 2 H), 5.66–5.56 (m, 1 H), 5.16–5.11 (m, 2 H), 4.16–4.10 (m, 2 H), 3.81 (td, J1  = 12.2 Hz, J2  = 4.7 Hz, 1 H), 3.54 (d, J = 12.2 Hz, 1 H), 2.92 (dd, J1  = 14.2 Hz, J2  = 6.7 Hz, 1 H), 2.84 (dd, J1  = 14.2 Hz, 1 H, J2  = 7.6 Hz), 2.67 (dd, J1  = 14.3 Hz, J2  = 4.7 Hz, 1 H), 2.29 (dd, J1  = 14.3 Hz, J2  = 12.2 Hz, 1 H), 1.14 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 167.9, 166.9, 143.2, 138.8, 133.6, 131.4, 131.4, 129.2, 128.7, 128.4, 128.0, 124.6, 120.0, 86.1, 61.8, 54.2, 47.0, 39.3, 38.3, 14.0. HRMS (ESI): m/z [M + Na]+ calcd for C23H23ClNaO4: 421.1183; found: 421.1174.
    • 10a This observation implies the stereoselection might occur at the Barbier reaction step through a plausible chelation effect involving the malonate moiety. This possibility is based on the observation that reaction in polar protic solvents such as EtOH gave no selectivity (Compare entries 1 and 3 in Table 1).
    • 10b There was no significant change in the diastereoselectivity with respect to the two diastereomers obtained from reactions performed for different times. Furthermore, the diastereoselectivity of the crude reaction mixture did not differ significantly from that of the pure mixture of diastereomers obtained after isolation by column chromatography on silica gel.