C O M M U N I C A T I O N S
ing product 13 in 75% overall yield as a single stereoisomer.
Regioselective hydrogenation of 13 in the presence of Lindlar
catalyst gave 14, which was then converted to 15 in high yield by
oxidation with DMP. Thus the final target maoecrystal V (1) was
eventually obtained in 48% (90% brsm) yield by the treatment of
15 with DBU in toluene at 100 °C for 1 h, affording a 1:1 mixture
of 15 and 1. Extension of the reaction time did not improve the
conversion of 15 to 1. The identity of the synthesized maoecrystal
V (1) was confirmed by comparison of the NMR spectral data with
that of natural product maoecrystal V (1).1
In summary, a concise total synthesis of maoecrystal V (1) has
been achieved by employing a Wessely oxidative dearomatization,
an IMDA reaction, and a Rh-catalyzed O-H bond insertion as key
steps. The developed chemistry may find use in the synthesis of
the analogue of maoecrystal V.
Figure 1. Synthetic analysis.
Acknowledgment. Dedicated to Professor Henry N. C. Wong
on the occasion of his 60th birthday. This work is financially
supported by 973 Program (Grant 2010CB833201), the National
Science and Technology Major Project “Development of key
technology for the combinatorial synthesis of privileged scaffolds”
(2009ZX09501-012) and the National Science Foundation of China
(20821062, 20832003, and 20902007), and the Shenzhen Basic
Research Program (JC200903160352A).
of 11a with LiAlH4 in THF, the diastereselective synthesis of cis-
diol 6 was eventually achieved in 88% yield.
We next shifted our attention to make precursor 3 of the proposed
IMDA reaction. In that event, cis-diol 6 was coupled with
2-(diethoxyphosphoryl)-acetic acid in the presence of EDCI and
DMAP to afford an ester in 85% yield, which was then treated
with TsN3 in the presence of DBU to give the diazo ester 5 in 69%
yield in two steps. Diazo ester 5 was subjected to the Rh2(OAc)4-
catalyzed O-H bond insertion12 to give 4 (60%), which underwent
consecutive Horner-Wadsworth-Emmons reaction with paraformyl-
aldehyde13 and deprotection of the MOM ether under acidic
conditions, leading to phenol 3 in high yield. In the process of
preparing the key intermediate 2, phenol 3 was subjected to the
Wessely oxidative acetoxylation,2a,3 affording stable o-quinol
acetates as a pair of diastereoisomers of C16, which without
purification underwent IMDA reaction in toluene at 145 °C to give
a separable mixture of products 2a, 2b, and 2c in 28%, 12%, and
36% yield, respectively. The structure of 2c was unambiguously
confirmed by X-ray crystallography.
Supporting Information Available: Experimental details. This
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a Reagent and conditions: (a) NBS, (PhCO2)2, CCl4, reflux, 2 h, 90%;
(b) Bu3SnH, TEMPO, PhH, reflux, 2 h, 75%; (c) Zn, AcOH, THF, H2O,
70 °C, 2 h, 85%; (d) SmI2, THF, MeOH, rt, 10 min, 88%; (e) Lindlar cat.
MeOH, THF, rt, 2 h, 92%; (f) DMP, CH2Cl2, rt, 1 h, 88%; (g) DBU, toluene,
100 °C, 1 h, 48% (90% brsm).
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(Scheme 2). This bromide was treated with Bu3SnH to generate an
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16746 J. AM. CHEM. SOC. VOL. 132, NO. 47, 2010