The stereoselective synthesis of cis-/trans-fused hexahydropyrano[4,3-b]chromenes via Prins cyclization trapping by a tethered nucleophile.
Subba Reddy, B. V.; Jalal, Sayed; Borkar, Prashant; Yadav, J. S.; Reddy, P. P.; Kunwar, A. C.; Sridhar, B.; Organic & biomolecular chemistry 10 (2012) 6562–6568; doi:10.1039/c2ob25771h

data_7152526
_publ_section_title
;
 The stereoselective synthesis of cis-/trans-fused
 hexahydropyrano[4,3-b]chromenes via Prins cyclization trapping by a
 tethered nucleophile.
;
_journal_issue                   32
_journal_name_full               'Organic &amp; biomolecular chemistry'
_journal_page_first              6562
_journal_page_last               6568
_journal_paper_doi               10.1039/c2ob25771h
_journal_volume                  10
_journal_year                    2012
_chemical_formula_moiety         'C20 H22 O4'
_chemical_formula_sum            'C20 H22 O4'
_chemical_formula_weight         326.38
_chemical_name_systematic
;
(1R*,4aS*,10aS*)-1-(3,4-dimethoxyphenyl)-1,3,4,4a,10,10a-hexahydropyrano
[4,3-b]chromene
;
_space_group_IT_number           14
_symmetry_cell_setting           monoclinic
_symmetry_space_group_name_Hall  '-P 2ybc'
_symmetry_space_group_name_H-M   'P 1 21/c 1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method           SHELXL-97
_cell_angle_alpha                90.00
_cell_angle_beta                 111.313(1)
_cell_angle_gamma                90.00
_cell_formula_units_Z            4
_cell_length_a                   12.8286(7)
_cell_length_b                   12.1802(7)
_cell_length_c                   11.4263(6)
_cell_measurement_reflns_used    9913
_cell_measurement_temperature    294(2)
_cell_measurement_theta_max      27.99
_cell_measurement_theta_min      2.39
_cell_volume                     1663.31(16)
_computing_cell_refinement       'SAINT (Bruker, 2001)'
_computing_data_collection       'SMART (Bruker, 2001)'
_computing_data_reduction        SAINT
_computing_molecular_graphics    'SHELXTL/PC (Sheldrick, 1990)'
_computing_publication_material  SHELXL97
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 2008)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 2008)'
_diffrn_ambient_temperature      294(2)
_diffrn_measured_fraction_theta_full 1.000
_diffrn_measured_fraction_theta_max 1.000
_diffrn_measurement_device       'Bruker SMART APEX CCD area-detector'
_diffrn_measurement_device_type  'CCD Area Detector'
_diffrn_measurement_method       '\w scan'
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_source         'fine-focus sealed tube'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0169
_diffrn_reflns_av_sigmaI/netI    0.0121
_diffrn_reflns_limit_h_max       15
_diffrn_reflns_limit_h_min       -15
_diffrn_reflns_limit_k_max       14
_diffrn_reflns_limit_k_min       -14
_diffrn_reflns_limit_l_max       13
_diffrn_reflns_limit_l_min       -13
_diffrn_reflns_number            15572
_diffrn_reflns_theta_full        25.00
_diffrn_reflns_theta_max         25.00
_diffrn_reflns_theta_min         1.70
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    0.090
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            colorless
_exptl_crystal_density_diffrn    1.303
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       block
_exptl_crystal_F_000             696
_exptl_crystal_size_max          0.18
_exptl_crystal_size_mid          0.15
_exptl_crystal_size_min          0.09
_refine_diff_density_max         0.145
_refine_diff_density_min         -0.151
_refine_diff_density_rms         0.032
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.047
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     219
_refine_ls_number_reflns         2927
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.047
_refine_ls_R_factor_all          0.0358
_refine_ls_R_factor_gt           0.0327
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0515P)^2^+0.2672P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0900
_refine_ls_wR_factor_ref         0.0938
_reflns_number_gt                2641
_reflns_number_total             2927
_reflns_threshold_expression     I>2\s(I)
_cod_data_source_file            c2ob25771h.txt
_cod_data_source_block           al66
_cod_original_sg_symbol_H-M      'P 21/c'
_cod_database_code               7152526