One-pot Selective Formylation and Claisen Rearrangement on Calix[4]arenes

Abstract

A versatile synthon with formyl and allyl groups at the upper rim of calix[4]arene has been synthesized in two steps. Selective formylation of 25,27-diallyloxy-26,28-dihydroxycalix[4]arene, along with the Claisen rearrangement of the allyl groups, was achieved by reaction with hexamethylenetetraamine (hexamine) in glacial acetic acid. A control reaction of the dipropyl analogue shows that the selective formylation takes place independently of the Claisen rearrangement. The crystal structure of the dimethylacetal derivative of 5,17-diformyl-11,23-diallylcalix[4]arene is reported.

Keywords:

• Calixarenes
• Formylation
• Claisen rearrangement

Acknowledgement

We thank L. T. Byrne for NMR spectra and helpful discussion relating to these.

Notes

C₄₀H₄₄O₈, M _r = 652.8. Triclinic, space group (C ¹ _i , No.2), a = 10.384(1), b = 12.844(1), c = 13.871(1) Å, α = 98.615(2), β = 108.600(2), γ = 99.084(2)°, V = 1691 Å³. D _c (Z = 2) = 1.282 g cm^− 3. μ_Mo = 0.9 cm^− 1; specimen: 0.35 × 0.14 × 0.11 mm; T _min/max (multiscan correction) = 0.91. 2θ_max = 55°; N _total (full sphere of CCD instrument data, T ca. 153 K) = 19258, N _unique = 7819 (R _int = 0.027), N _obs (F>4σ(F)) = 5408 reflections; R = 0.056, R _w(weights: (σ²(F)+0.0005F ²)^− 1): = 0.064. (x,y,z,U _iso)_H constrained at estimates, OH modelled as disordered (see Fig. 1) from difference map evidence. |Δρ_max| 0.46(3) e Å^− 3. CCDC: 253375

The acetal was unstable in CDCl₃ and decomposed to the formyl derivative (3) fairly rapidly. The ¹³C NMR spectrum contained signals due to the formyl derivative even though the ¹H NMR spectrum obtained immediately beforehand showed the product to be the acetal and no signals attributable to the formyl derivative were observed. However, the proton spectrum of the same sample, obtained immediately after the ¹³C NMR spectrum was recorded had a significant signal for the formyl proton. The CDCl₃ was passed through basic alumina prior to use.